Despite what Ganin (socionics.com) says, INTP (MBTI) and INTj (socionics) are the same thing.
They both have as base function and as creative function. MBTI gives a much better description of my type than socionics. MBTI also allows me to know my type without any difficulties. There is no point to socionics if you can't find out your type - if you are looking for your dual in socionics, you could end up with your conflicting relation!
I think that intertype relations of socionics should be applied to MBTI, so that MBTI INTP and ESFJ are duals.