Yeah, you should just SLi that 8800GTS then. If it was the 320, I would say no, but the 640 should be fine. You might get lower minimum frame rates than just going with a single 280, but it should still be a pretty good increase. Looking at the charts though a single 8800GTS 640 only gets like 17fps at 1920x1200, 0xAA, 0xAF, High Quality. I think if you SLi your cards you should be around 28fps with no AA and no AF at 1920x1200 on High quality. If you want to run Very High, then you're probably going to have to buy two 280s at the least.