Budget SLI vs. One Higer-end Card?

I'm in need of a new graphics card but I'm debating whether I should get two low end cards and put them in sli or just get one better card. I'd probably be looking at two Nvidia 8600gts 256mb or one 8800gts 640mb. Both of these setups would cost about the same price for the cards. I'm not really interested about that fact that if I get one 8800 now I'll being able to upgrade to two later or the different power needs of both. I'm mainly looking at which setup would give me better performance. The SLI 8600 would be cool just cuz it's SLI but it would only have a total of 512mb memory vs the 640mb of a single 8800, but would the dual computing power of two 8600gts' be better than a single 8800gts?

Thanks

A single HD2900XT.

With SLi, you don't add up the memory of the two cards.

Single High-End. End of story.RoganSarine

A single high-end card is always the better choice.

Multi-GPU configs or in the case SLI has problems mostly with games is because of its drivers. Much less to say that SLI in Vista now is just well.... crap.

Going for a single high-end card even saves you more money and also more importantly, gives you the same performance or even higher performance. Also, a single card uses less power than SLI configs.