Re: Which is better dual 6600GT, or single 6800GS
(I'm only talking single cards in this post.)
The thing you should remember is the 6600GT only has a 128bit memory controller where the 6800GS has a 256bit memory controller.
The 6800GS also has more pipelines to start with.
It's a better card overall.
At this point, even if you aren't going to go SLI, the 6800GS is a much more capable card.
If you have a 6600GT now, sell it and get the 6800GS.