I actually decided to go over and compare the demons in FCI and the ones that I personally converted. Surprisingly, I liked only 1 of my conversions 'better' than the FCI versions: the Chasme.
A few others I preferred bits and pieces of from mine (parts of the Molydues for example), but most of them, I really liked the official ones better.
Wow...now I'm really embarrassed/ashamed. The kind folks on the Rules forum pointed out that on p. 171-172 of the Player's Handbook, this rule is described, and even uses ray of enfeeblement as an example.