Right now, there isn't that much of an importance of the SM 3.0 (in my knowledge) but if your getting into games that uses Open GL, by in large, get the 6600 GT since it will get the upper hand. But...in some cases, the X800GT will by far outperform (in my knowledge by the specs that it has) in many games than the 6600 GT (like direct 3d games : UT2k4, farcry, etc). Because.... the X800 GT will have a 256 mb onboard ram (great for games that need lots of room for textures "eye candy") and also 256 bit interface (whereas the 6600GT has 128 bit memory). Either way you can't go wrong in either one, but for the moneys worth, stick with the X800GT
