In general, Ones as a group are extremely idealistic and highly moral. Often to the point of compulsion, actually. Eights never occur to me as "controlled", even the w9s. And usually either amoral, or follow their own personal version of morality, but undefined as such.

Ones have a very rigid kind of persona that they naturally default to. Eights seem much more comfortable with themselves. Also, I've never found Eights to be introverted. Not that one could never be, but IME, they simply aren't. Eight energy is not introverted. One self-control lends itself more naturally to introversion at times, although I've known I as well as E Ones.

This may help clarify also:

"Perfectionists and Protectors can be considered "look-alike" types because both are Body Center (gut) types and are concerned with rightness, justice, truth and fairness. Protectors (8s) however, state their truth openly, express their anger directly, and go from impulse to action easily. Perfectionists (1) suppress anger and impulse, becoming resentful and tense until a sense of righteousness allows their anger to spill out."

The Essential Enneagram
David Daniels/Virginia Price
Inhibition seems to be the key word for me in telling these types apart. Eights are not inhibited; Ones are. How you deal with anger is usually a good differentiator.