The GTX 570 is better, but $50 more, consume double the power than 7850 and run hotter compared to the 7850. In my opinion, get the 7850, the little performance increase on the GTX 570 is not worth it seeing that it is more expensive, power hungry and heat. So get the 7850 (or the 7870 if you can) and if you want nvidia, wait for the mainstream kepler, which looks promising by looking at the 680. It could be the 660 or 670.
I agree with you, I think the difference between there performance isn't enough high to cost 60$ = )).I'm looking forward to Kepler models,it realy sounds intresting. but i'll get 7850 if they doesn't release soon = ))