580's are still friggin powerful as people have said. Sure the 7970 does perform awesomely, but even GTX 580's should last a long time.
One more thing - AMD is currently having issues with DX 11 on the 7970 video cards, they are performing almost worse than the 580's right now....should be fixed with a driver update down the road.
One last - last thing - AMD has been having major issues with driver updates for CFX and games, they weren't on the ball last year. Single GPU performance is good, but CFX is a sore issue for them ATM.
BTW i'm not a fanboy of either GPU makers - I like to give honost information. Although I do lean a little to the red side
Nvidia right now - Good driver support, good cards.
AMD right now - Best GPU in town, mediocre driver support (concerning DX 11 and CFX).