I am recently in the market for some improved performance graphically and I'm a bit torn on which direction I should go. Here is my current setup:
MOBO: Asus P8P67 Pro
CPU: i5 2500K
RAM: 8GB RipJaws DDR3
HDD: 1TB 6gb/s WD HDD (40GB intel SSD for OS)
GPU: HD Radeon 6970 2B (from Diamond)
On one hand, I could go cheaper by buying a second HD Radeon 6970 and XFiring it but I'm a bit new to the whole dual GPU world and, quite frankly, I'm not even sure if two 6970's will even fit on my Asus mobo. On the other hand, I've heard great things about the GTX 680 and wouldn't mind dropping some extra cash if it meant better performance than doubling up on the 6970.
To be clear, my goal is to be able to run the game Rift (an MMO with an expansion dropping this November that uses new Shroud technology for fabrics and quite a substantial array of particle effects and excellent lighting techniques) completely maxed in all regards including their Supersampling AA. At present, with my lone 6970, I can run the game on Ultra settings at a comfortable 30-50 FPS but am not able to turn on any custom AA (they have two levels: Edge Smooting and Supersampling) or my FPS drops below 20.
Well lets say the GTX 680 almost beats a 6990, which is effectively two 6970's in most games. GTX 680 is almost double the performance, and you could probably overclock past that point as well.
6970 Crossfire is good, but a 680 would probably suit your needs more in that case, although you can also get a 670 and overclock it there as well. A good factory overclocked 670 is = to a stock 680. I would recommend a 670 or a 7970.