Sli is pure marketing hype.
Is just makes sense if money is no problem and if you want to pair up two ultras now (not later or next year) to get the most speedy gpu that is possible. If you buy 6600gt and pair them up you will perform slower then a single 6800ultra, because its not scaling like 1+1=2 gpu, its more like 1+1=1.8. Driver Improvement could enhance this calculation but by the time drivers mature the next gen vga cards will be out.
And: you need 2 6600gt = 400$ = a single 6800gt
A 6800gt can clock to ultra speeds, so there is no point in getting 6600sli.
And you need a pricey unmatured double pci-e board. After all you spend more money than others for less performance.
You can go out and buy two 6800ultra on the other hand, so you are basically throwing 1k out on vga cards. While it is just crazy expensive and its unsure up until which point you have the performance crown in your hands this path certainly makes more sense than the 6600 sli rubbish.
Buy a single card, trash it at ebay if you don't need it and buy the next card. That is the structure of update evolution i will follow, and sli won't change a thing on it.
Besides: check out nvidias 3dmark05 propaganda sli numbers, are they near the "double the performance hype"?
