Right now two 7900GTXs in SLi is the best dual slot setup hands down, there is no real performance gain of 16x vs 8x although newer dx10 cards could change that...crossfire is good and getting better but SLi puts more power to the ground...i say this because a signgle ATi X1900XTX will beat a single 7900GTX, but two 7900GTXs will beat two X1900XTX , all of this is irrelevant if you game under 1600x1200 or 1920x1200 for that matter, that is where dual gfx card setups really kick in, unless your playing Oblivion