Two 680's should work. For some of the really heavy games, like Crysis, it will not be enough for the highest presets, and you might still have dips in some BF3 scenes on Ultra settings, but in general it should play smoothly. However, if you have not bought any cards, you might want to consider 3 660's in SLi. This usually performs better than 2 680's, and it acn even be cheaper if you buy them smartly. However, building a triple SLI system is much harder, so take that into account