I have made more with Mostphotos, Panthermedia and Rodeo, all midstock sites.
I had quite some sales on Mostphotos too, April-May last year, when everybody had about the same rank. Nothing since then, but my rank is still around 50 and yours around 1030. That means you've spent a lot of energy on commenting and stuff. That's no critique by any means but it illustrates the fact that the social networking, grooming and shoulder-tapping aspect there is more important than the intrinsic value of the photos to get on the front page (and sell).
Cutcaster is OK but I feel the few sales there are just random hits by a very limited buyers base.
FeaturePics was very OK till half last year, then came to a sudden stop for me. Like any similar oddity, it probably has to do with the search engine. On some sites, you are the search engine's darling and you don't know why. On others, you just don't get airborne.
Zymmetrical: better than all 4 for me the past year, considering I just uploaded 1/2 of my port. But 2/3 of my sales there are people shots in situation,
not (except 1) in studio set-up. It might be portfolio-dependent. Just wait and see who will survive. For them it's as tough as for us to survive in a market with too many suppliers.