6670 doesn't offer much over 5670.. I'd say go for 5750 or 5770, they are pretty cheap these days. I think this article will help anyone looking for some guideline to buy a graphics accelerator. http://www.tomshardware.com/reviews/best-graphics-card-game-performance-radeon-hd-6670,2935.html
gpureview.com/show_cards.php?card1=654&card2=623 6670 seems a bit better but for that price i'd go w/ the 5770 of even 5750 gpureview.com/show_cards.php?card1=654&card2=616
I'd like to add that if your budget permits, go for AMD 6790. It offers same performance as GTX 460 (Even better is some cases) at the price of GTX 550 Ti (pretty cheap mid range card). And to everyone just shouting 'Da ATI 6670 is Da best!!!!111oneoneone", please do yourself a favor and read something about current graphic card market trends. First of all ATI doesn't exist anymore, its AMD. And 2nd, no 6670 is not "Da BEST" card. Its not even a better one, for the almost same price you can buy AMD 5750, which offer a better performance or even 5770, which is way better.
Whatever you purchase their will always be a game that wont run with your graphic card. always remember to turn the setting of graphics to low if is a good graphic game. Did any one ever play Hot pursuit 2011.