The GeForce 6600GT seemed to scale reasonably well, with a pair of 6600GTs outperforming a single 6800 Ultra in Doom 3 and Half Life 2. It doesnÂ’t make too much sense to buy a pair of 6600GTs today however, as youÂ’d be much better off getting a single 6800GT and upgrading to a second one down the road, which brings us to our next point, the upgrade value of SLI.