Originally Posted by Thunderbird
In theory you can get twice the performance when using SLI but in practice this is quite a bit lower and it depends on what programs you use. SLI can be nice if you buy a card now and later on add an extra card to boost performance or if you want the highest performance there is you can bundle the two fastest cards (geforce 8800 boards).
I wouldn't recommend SLI as in general you can buy a much better single card for the same amount of money. I would invest in a nice Geforce 8800 board.
My experience with x86_64 large memory (8Gb) dual dual-core machines is that SLI is nowhere near as stable as running with a single card. Also take a serious look at Quadros. The performance of the Quadro 4500 compared to a 7800GTX can be *astounding* in some applications.