I get higher FPS in Win 7 than I ever got with XP. Make sure you disable Aero -- select the Windows Classic theme through the appearance control panel area for a fast theme. The only other thing I did besides disabling Aero was download the current nvidia drivers, but it sounds like you already did that. Other than that, high performance settings in WoW and I get a fairly consistent 20 FPS with 5 in Dalaran as opposed to 10-15.