The 7970 is a great card. However, it is priced a little off in the mid $400. $400 will get you a GTX670 which in most cases runs with a 7970, depending on the game. There is a GHz Edition 7970 that runs closer to the GTX580, but I think it's priced a little under so it might be a better deal. It's almost a preference at that point and could depend on the games you play. Some games favor AMD others Nvidia. I have found AMD driver to be more temperamental than Nvidia's. So lately I've stuck with Nvidia.
For $400 you can't beat the GTX670, hands down.