the thing about physX is that next to nothing uses the nvidia cards for it, ever game loads it onto the cpu so they don't look bias towards nvidia customers and everyone gets an equally satisfying experience, meaning they get more money. as for which brand is more powerful it goes to the price point. amd just about owns it up to the 560's, which i think they are about equal with, then the 6950 is slightly better, but not enough to say it is a better buy, the the 570 is a little bit better but the 6970's extra vram gives it an edge, then the 580 has no competition and i have no clue on 590 v 6990