I am split between getting 670 or 680 SLI, or a 680 or 7970 GHZ single card. Ive heard bad things about crossfire, so i wont be considering that. I will be going with 1920x1080 and want to run Crysis 3, Far Cry 3, and Skyrim at GOOD fps, not great, just want over 40. is SLI worth it?