DirectX 10 or 9? In the NVidia control panel, are most of the relevant setting, set to application controlled? Last I read, SU still prefers how DirectX 9 and OpenGL play together. Setting hardware acceleration (anti-aliasing, antisotropic too) to application controlled overcame a DirectX 10 issue with one 8000 series NVidia user.

Have you tried unchecking fast feedback in Window/Preferences/OpenGL?

You can check how DirectX is feeling: Start/Programs/Accessories/ System Tools/System Information/Tools/DirectX diagnostic tool. It's