I use my GTX 560 Ti on Skyrim to play it on max settings with around 45-50 fps. Also, Battlefield 3 works on Ultra with MSAA x2 single player. Didn't try multiplayer since I only play those kind of games for the story (which sucked tbh ).
both 6970 and 570 will do fine.it depends on games you play.some games perform better on radeons whereas some perform better on nvidias.go which you find cool and
cheaper.i would suggest MSi cause i am a bit partial for them(not a fanboy)cause they have really good cooling and overclocking IMO.
I mean, by all means go for the 570 or 6970 if you have $350 laying around.
I'm just saying your performance won't be dramatically better than a card that's 35% cheaper. After the 560ti you hit diminishing returns - 50% more in price for 12% more performance just doesn't make sense to me.