I've got a BFG 7800 GTX, looking to go SLI soon. I've looked on the forums and at other sources, and haven't really seen any info saying "You can't mix card X and card Y." My question is...are there any cards (fromt the same GPU) that you can't mix for SLI now that the new drivers are out? It may seem like a dumb question, but I'm really being overcautious- don't want to make a bad purchase.