Just had to sign up to say thank you!, you saved me a whole lot of frustration, I'd just got my second GTX 470 and could not figure out why SLi would not enable, then I notoced my MB was the wrong chipset AMD GA-MA790FXT-UD5P, I was just about to pull my hair out when I found this thread, now I won't be bald!
Skyrim is still cruddy even with SLi, but no surprises with that engine, Mafia II got a massive performance boost, almost doubled the framerate and I can now put Crysis on ultra!
I have to say it again, thank you very much for your efforts and sharing, you're a star in my book.