Ocean Moonshine's site has an extensive discussion of possible mistypes (click on any of the types and possible mistypes with every other type discussed.) Here is what he says about distinguishing the 5 from the 3:
Intellectual Threes can sometimes mistype or be mistyped as Fives. The
sociobiologist Steven Pinker is an example of this. But contrast his open,
expansive, self-promoting style with that of E.O.Wilson (his fellow
sociobiologist at Harvard University) in order to recognize the difference.
Wilson, a Five, is self-effacing and almost shy in person, although he is as
certain of his ideas as is the more famous Pinker. In general, Threes are more
self-confident, optimistic, image conscious and socially competent than are
Fives. Fives tend to be more intellectually innovative, personally
idiosyncratic, reclusive and emotionally sensitive than Threes.
Good stuff. The only part of this that surprises me is ... the assertion that Steven Pinker is more famous than Edwin O. Wilson. I am posting a poll where you can vote. Choose between: Steven Pinker is more famous, Edwin O. Wilson is more famous, or I have never heard of either of them. If you have heard of both of them, choose one as being the more famous. Go with your gut. If you've only heard of one, obviously, the choice is easy.
Meanwhile, I'd like to recommend the book How the Mind Works by Steven Pinker. Fascinating. It changed my thinking. If you are an Enneagram enthusiast, I imagine you are interested in how the mind works.