Just thinking out loud here. You say 500Kh/sec (maybe you made up this number?). The low end "good" GPUs today are about 300Mh/sec. So you would need 600 of these chips to equal one GPU. Is that really going to be feasible in terms of h/$ and/or h/W.
It's a made up number, I don't know the performance of those chips. It may take more, but they'll still use less power.
Another alternative is to buy ATIs development hardware and make a board that uses the GPUs purely for computation.