two 6600GTs is a total waste. It preforms about as well, usually a little worse, than a single 6800gt, and costs as much or more than a 6800gt. Plus, if you get the 6800gt, you are still leaving one PCI-E slot open for possible SLI in the future. And the x850xt preforms a little better than the 6800gt, except in openGL games where the 6800gt does better. But the x850xt is a MUCH better choice than the 6600GTs. Between the 6800gt and x850xt, its a closer call, but if you dont plan on ever adding a second 6800gt to SLI in the future, then the x850xt is a better choice. If you do plan on adding a second 6800gt (keep in mind thats $700-800 you would be spending on the two cards) then it would destroy a x850xt, but its also quite a bit more money.