I have never run SLI or Crossfire, but I have had several SLI motherboards. It really doesnt matter if it has that option, just get a good motherboard.
But I agree with Subman on the HD 4870, its incredibly powerful, and clearly more bang per buck than any of the current from nVidia. You have a 6800 now, no? I would say the 4870 is 300-400% faster. I pulled those numbers out of my behind, but it will be awesome for you to upgrade now, it will be night and day.
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