Envy is supposed to be a characteristic behavior for 4s, but many 4s may not be aware of it, or even manifest it in the sense of the traditional meaning of the word "envy." So they might think that they must be sevens because of what they see as a lack of "envy" of other people. But actually, the term "envy," as used by Riso and Hudson, could be simply longing to be something that they are not, the "envy," in the sense, of the ideal. Because the type 3 is out of touch with its feeling center, and thinks that the image it constructs and projects for itself is itself, the 4w3 is someone affected by this. They may not even realize that they are the way they are because they want that image. Riso and Hudson use the word "envy" almost as a kind of term as the desire to be something other than yourself, in a way that actually makes you change your own internal identity. Only when 3s become healthy are they concerned with real authenticity in their image, and only when 4s become healthy can they accept and feel their true inner identity, unsustained by any external symbols, labels, or characterizations.
Behavior vs. Core Fixation
The Enneagram tries to layout the behavior of each type as it is in general, then tries to talk about how the type is at different levels of health, with different wings, and with different instinctual variants. So, with that taken into account, you may fitting the description of a 4w3, augmented by the 5 wing, the sexual/self-preservation variants, and varying levels of health. Each of these augments the descriptions of the 4, and pulls out things that would apply more to you because of your unique secondary characteristics, while points out other things that would fit you less, due to the same characteristics, all created by the same core fixation.
The main observable difference between 4s and 7s is in the 4's emotional longing vs. the 7's energized but shallow interest:
"Fours...cherishing beautiful objects of the sake of their beauty and the feelings that beauty awakens in them. A stone picked up on the beach or a twig with a single bud can quicken their aesthetic feelings and satisfy them. By contrast, while average Sevens want to possess beautiful objects, they become increasingly unappreciative and insensitive to the beauty or value of those objects. They become acquisitive not because they enjoy things for themselves but because the acquisition of possessions provides a sense of security. And even more fundamentally, what excites Sevens is the stimulation they feel when they desire something new. The stimulation of their appetites reinforces their sense of self, although once they have actually acquired what they want, they usually lose interest in the acquisition. The pair of shoes that they were "dying" to have join the racks with a dozen so others; the fur coat they were drooling over for weeks suddenly becomes "that old thing" as they turn their attention to acquiring something else." - Riso and Hudson, Understanding the Enneagram, "Misidentifications" section.
As Riso and Hudson also said at the beginning of Understanding the Enneagram, no one manifests all of the behaviors of one type, so it is not even expected that you would fit every description of the 4 or the 7, just the core ones. The 4 will experience a real appreciation of beauty (in things, fantasy, emotions, etc.) vs. the 7's fleeting materialistic interest. This is the core difference between me 4s and 7s, because most 7s you meet will only be average health and will show this problem.
Because of this essential difference, a 4w3 may be able to see that that their claims to 7 and their problems with the 4 are explainable by variations of the 4, while their problems with the 7 are not explainable by variations of the 7. This deep, intense, prolonged "longing" connected to a fascination with fantasy ideals, like a theme in their life, is not explainable by any of the variations of the 7--wings, variants, or states of health. Because they feel so close to both 7 and 4 characterizations, because they do this, their core inner focus is more on identity than stimulation. The same thing could be said, incidentally, to a 4 trying to figure out whether they are a 4 or a 5, as 5s have many 7-seeming issues.
At the end of the day, the thing that truly makes a 4, according to R&H, is the desire to be true to oneself. This fixation is the direct result of the core need of identity. 7s and 7-wingers may indeed be NFs, a characteristic which has nothing innately to do with identity issues. They don't have the issues around the desire of being yourself and being understood like 4s do. 7s and 4s just have different fixations. All the NF does, the extroverted intuition and introverted feelings of the ENFP, more common to both types, is makes them notice threads of meaning and scan for what could be, and makes them have an internal sense of the "essence" of a person or a project, reading them with fine distinctions among feeling-tones. The NF quality does not induce the development of identity needs. Being a 4 does.
Sexual 7s vs. 4s
It may be said that a sexual variant in any type makes them seem more 4-like, with more idealism and feelings of longing and fantasy. But sexual 7s will still display all the characteristics of shallow disinterest with a thing they were just a minute ago so happy about, everything R&H has said about them was still true for them. Even my super-creative and even melancholy-seeming observed 7 could be taken for a 4 in the sense that he is melancholy, but when you really look at him you see that he has the same problem with a prolonged appreciation of beauty. For an observed 7w6 it was found that, although he can get interested for periods of time and create wonderful works of art, he quickly gets this depressive sigh about it, and is utterly uninterested, an astoundingly sudden and complete change.
If you compare the core problem of the 7 to the core problem of the 4, they will always be able to tell each other apart. An observed 7-winger is a classic example as well, a 6w7 who seemed incredibly grave and melancholy many times, many of the outer qualities which you might think of as 4 qualities, but he has the same core problems as the 7-wing as described so importantly in the Misidentifications section. And as much a 4s may identify with the observed 7-winger so well in their depth in other areas, in this area he really does have problems. He has the 7ish problems with prolonged appreciation of the beauty of one thing. He'd fool you because he always talks about his sentimental appreciation of systems or people in his life that keep him secure, as he is an NF, but when it comes to being able to be engaged and appreciate something entertaining, he becomes 7ish. Quickly utterly and shallowly disappointed, this kind of shutter and sigh comes out of him, that it's just old now. It's so fascinating to observe Michael Scott from The Office, and watched him have incredibly similar reactions. When you watch Michael get incredibly excited and then, like, oh this s*cks, that is characteristic of average 7s, although exaggerated and he's probably exceptionally unhealthy.
7s and Shallow Disinterest
Some people may take offense to the characterization of the 7 as "more shallow" than the 4. But the differences aren't really that superficial. 7s can be deep or creative, like the observed 7 and 7-winger. Like said in the misidenfications area though, there are certain instances where problems with focus exist, and it is, like R&H said, an important distinction. And, 4s, being around creative 7s, as much as they might feel connection to them, when it comes to the same obsession they have over amplifying and drawing out idealistic, intense feelings and experiences, the 7s do not join in with them. To this, the 7s may feel more "shallow" to the fours, because their interest in things is not able to be idealized and romanticized in such a prolonged passion as the 4 has for it. They just have different core needs, as R&H pointed out, so they are fueled by different things, and therefore pursue and experience the same source of enjoyment differently. In the end, an average's 7s focus may be characterized by intial intense excitement, followed by a sudden and utter shallow disillusionment and disinterest. It as if it has suddenly become old to them.
Let's take one 7w6 who has been observed for many years. He's pretty healthy, and has integrated to 5 somewhat, because he can learn anything just about seemingly instantly, though at times you can see him disintegrating. Life is all about present stimulus for him. He gets interested in computers, he spends alot of money buying the latest one on the market, spends a deal of time on it, then completely looses interest. There is almost a pessimism he views his computer with now. While others were fascinated by it, and he seemed kind of disappointed just by looking at it. "Oh yeah, that old thing," he seemed to say, with depressive frustration.
He got interested in piano as a child, became an excellent pianist. Can play anything just by looking at it. He created an self-made album. Now he looks at the piano with the same depressive frustration.
He became interested in painting around the time his father died, spent several months painting from scratch. Became an excellent painter seemingly instantly. But now he looks at it with boredom when you mention it, almost as if saying, "Well, THAT doesn't stimulate me any more."
He bought an excellent house a few years ago. Was really excited, decorating, taking care of the pool, getting involved in the community. Now he seems to take it all for granted. Kind of lays around and sighs until you mention something that might interest him, and gets incredibly excited.
That horrible boss Michael Scott on the American version of "The Office" was typed as a 7w6. I did a research project on him for one of my senior projects, recording his behavior as he did it, and I was amazed at how many of those same depressive looks of frustration he gave to things after seeming so excited about them perhaps only a minute ago. Very good acting; I think that character is a part of him, somehow. The observed 6w7 is also frequently caught giving those same looks to things that once brought him stimulation. It is like a spoiled child with a broken toy. Utter shallow, disappointed disinterest.
7s vs. 4s in Melancholy, Depth, and Creative Expression
7s who entertain like Robin Williams and Jim Carrey are not the only forms of 7. The observed 7w6 seven described earlier is incredibly creative and talented, and not as much the over the top entertainer, possibly due to his sexual variant. But he still faces all the issues of focus and detachment Riso and Hudson describe, as are also described earlier. This characteristic of more integrated 7s does not detract from their characteristic problems with focus, which are only more visible when they are in average to unhealthy levels.
The 7s' creativity can definitely be characterized with a different terminology than 4s. When a healthy 7 becomes focused, it is still with a more realistic and pragmatic sense than a 4, not being energized by the idealistic and fantasy aspects so much as the purely stimulative ones. This is an important difference, as it shows itself even more when 7s disintegrate and loose their ability to stay with the stimulus. Even the Myers-Briggs common 7 equivalents tend to be more action-oriented, realistic, pragmatic entertainers and quick-witted innovators. Realism in art is a little different, but it may be able to serve as a pattern.
Leonardo DaVinci has been typed as a 7 integrated to 5, a man who become an expert seemingly quickly at anything he picked up, able to focus intently on things for a time. But, if he is typed correctly, there would also be more of a realistic, pragmatic element to his focus, compared to an integrated 4. And there is seen in his work an extreme element of realism and focus on the smallest detail. The problem is, since none of us can know Leonardo, none of us can correctly tell what he was like at all times. A person existing in real life can be observed, though. The observed 7 was used as an example because, perhaps like Leonardo, he had integrated to 5 at periods of his life, and produced wonderful works of art and music for the time that he was stimulated by them. It was also observable, though, that as he disintegrated, he became easily beset by a sudden and shallow disinterest, as described earlier. It was not fantasy or emotions that stimulated him, even now, but the novelty and intricacy of the details associated with a thing.
That's why the 7 integrates to 5, perhaps, since type 5s are characterized as detached, analytical observers. But the part that makes the integrated 7 five-ish is that their normal capacity to become stimulated by a new source is a now focused and intense observation, like a 5's. Much of a 4w5's relation to a 7 is obviously through their 5 wing. They see themselves being like integrated 7s in that they are able to absorb information and become an expert in many areas, and that when disintegrated they are like scattered, stimuli-hungry 7s. But the main difference is that the 4, even with a 5 wing, is characterized more by longing for an ideal, intense experience, and then sustaining that experience, fixating on it for long periods of time and reliving it, to sustain that fantasy, and then going out and seeking more. This pleasure, fantasy, and idealism focus is quite different from the real focus overall for 7s. The average 7--repeat, the average 7--is mentally inwardly saying, almost, "okay, I don't care, gimme stimulation. aw, it's old already. grrr. let's move on. okay, gimme more. aw, now it's stupid. moving on..."
4w3s Seeking Image Subconsciously
Type Three is characterized by Riso and Hudson as adaptive, excelling, driven, and image-conscious, traits which affect the psychological build of the identity-seeking 4w3. The 4w3 is driven to maintain the image of their identity. If they are fun-loving, they want people to regard them as that. The main problem observed with 4w3s becoming aware of this is that they are pursuing this goal of image is subconsciously. If they allowed themselves to see that they are not the carefree extrovert they regard themself to be, that they are regaled by identity and image issues, then their ego collapses into a depressive state. Because of this, average to unhealthy 4w3s can be seen as more brittle and yes, even psychologically more fragile, than the 4W5. The 4's usual fear of being "found out" for their essential flawed-ness is experienced beneath the level of awareness, with much potentially detrimental consequences.
Often, instead of letting this happen, they simply experience the pain from an unknown subconscious source. Once becoming aware of and trying to confront this source, the 4w3 may find themself trying to grasp at the source of their pain, and coming up with blanks. A classic scene is of one sitting all alone in the middle of the moonlight woods, staring off into nothing, knowing they had to confront something, but not knowing what. And somehow, even if a person knew exactly what to say to them, it would be almost impossible to say, because it would break their heart. It could easily bring the searching 4w3 into that depressive, nihilistic void that says "you are not who you say you are, even to yourself, and all is lost," because they were not ready for it, to experience that kind of pain and humility that would bring them to self-knowledge. The 4w3 may not be able to rise out of the resulting depression at having been "found out." It is so subconscious, even to themselves, that it can be a very dangerous admission to approach.