said by TRU:I wouldn't buy an AMD card seeing as how you already have a 670. If you're looking for more performance, you would be better off buying an additional 670 for SLI and gaining performance that way. Rather than ditching the 670 and buying an entirely different brand (AMD) when you already have your foot in the door with Nvidia and a phenomenal card to boot.
I'm not denying the 670 is a truly great card, but I am exploring all setups, at this point though a pretty good case has been made on my current setup for another 670.