[Aquinus]

Try upgrading from Windows XP. My 6870 before I went with crossfire got pretty decent frame rates on Skyrim on Ultra, I can't imagine the 6850 is that much slower. DX 10 and DX 11 have optimizations that DX 9 doesn't. There are also improvements to the CPU scheduler which might improve performance if Skyrim is fairly multithreaded. I'm convinced that your platform could be running faster just by running Windows 7.