"feel the fact most of the authors who come to mind are white and middle or even upper class"

Doesn't that describe most English language SF authors in general? If most SF is written by white middle class then most eugenics SF would be written by such by default.

I expected you'd have specified 'male' as well, but you didn't, so my bringing up MZB and Comyn eugenics seems less relevant. On the fantasy side, Hodgell's Kencyrath bred for Shanir powers for a long time, until they apparently started trying to breed them out. The Knorth were still fabulously inbred.