The 670 and 7970 perform basically the same at stock up to 1080p resolution, trading blows depending on the game. The 7970 most likely will OC better and it will murder the 670 at high resolution (and has way more compute power), the 670 gives you CUDA , PhysX, TXAA, FXAA, ADap. Vsync etc and lower power draw. Both are solid buys.If you still can't decide which card to take try looking at the games that you play or specific features that you want.If cost really matter to you then you might want to go with whatever is cheaper to you.
im liking the evga 670 but concerned about the temps of the card but that gigabyte 7970 with the 3 fans would do much better with cooling id imagine, the asus670 would match my build the most but alot of people are saying the rma is terrible with them and that they run hot so i am stuck at a predicament here