My thoughts on glute ham raises...

Well, between GHR and leg curls, I don't think there is a close comparison. Oh, and before we go further, I'm STILL working on completing an unnassisted GHR. They are a serious ball buster, but imagine the strength that your posterior chain has to exert to pull your body upright in such a fashion!

As for using a push-up assist, my thoughts would be that the push off should be just enough to get you through the motion. It is not hamstring assisted pushups If I was a wise man, and I can be from time to time, I would maybe look into using stretch bands to provide the assistance rather than your legs. I'll bet that if you hung them in reverse from a power rack that you would get a good assist off of the floor or bench that you were using (my training group tends to do these off the floor by hooking heels under a loaded barbell. I do them off of a bench that has a detachable pad that you are supposed to brace your legs on). I also have a good friend that does his "ghetto glute ham raises" by hooking his legs under the knee pad of a lat pulldown machine, and using a swiss ball to catch him at the bottom as well of providing something to push off of.

Alternatively I would perhaps look into using stiff legged deads or romanian deads as an alternative to leg curls. I suppose that at the end of the day leg curls/extensions are just not the most economical lifts. Not that they are evil or crap... but just aren't giving you the most bang for the buck is all.