Maxxing out games now is all very well, but what about when future releases require more juice?
I always suggest getting the best you can afford - that way you're covered for longer. The better your gear now, the longer it'll stay competitive for, and the easier it'll be to upgrade around it.
If you
can afford the 580 and all the requirements it'll pose, then why the hell not? You won't necessarily notice a massive difference between that and the 6970 now, but what about next year, or the year after? Buying the best you can increases your rig's endurance - it'll keep tackling coming releases for a longer time, and it'll be longer before you
have to upgrade again to stay on top/ahead of the curve.
For that res though, if price is a consideration at all, a GTX 570 or similar equivalent will do excellently, or you could consider SLI 460s or SLI 6850 for great performance, or SLI 560Ti's which are more or less on par with the GTX 580, for a slightly lower cost.
Use this article as a guide:
http://www.tomshardware.co.uk/best-graphics-card,review-32225-5.html
Also don't assume it's just the GPU that will tackle the games
You'll need other components to be strong as well, not just the GPU.
Good luck.
-Nih