there is a reason its called a 6800gt.........thats because it wasnt good enough to be an ultra, the 6800gt is fast enough as it is, ok i have mine at 400/1.1ghz sometimes but i only see a difference in 3dmark...if it will actually run.
overclockin it does nothing to boost 3dmark 2001 performance, nor do i notice any change in splinter cell or UT2004, jus leave it stock an be happy