I have two videocards in my system (NOT SLI/CrossFire): a 9800GX2 in Dual-GPU Mode and a 7900GTX for my second monitor. The problem is that any OpenGL based application (such as Blender, MeshLab, Stellarium etc.) runs horribly! All Direct3D content using DirectX9 or DirectX10 runs butter smooth. Why? I looked in Rhino 3D’s options menus, and it confirmed that it was in fact rendering all output on the 7900GTX graphics card even though the application was loaded on the primary monitor connected to the 9800GX2! Moving the window to the other monitor did not alleviate the problem, as the 7900GTX does not up-clock properly so the core is stuck at 275MHz (instead of 650MHz). The only solution I have found is to disable the 7900GTX if I need to run an OpenGL application. This has the unpleasant side effect of shutting off my second monitor. Then the application runs beautifully on the 9800GX2; however if the 7900GTX is there as an option, every OpenGL application tries to use it while simultaneously displaying on the 9800GX2 controlled monitor, resulting in aforementioned performance issues, which include excruciatingly slow rendering, applications “Not Responding” and applications using huge amounts of CPU time but ultimately freezing and requiring an End Process in the Task Manager.
My operating system is Windows Vista Ultimate x64 Service Pack 1 with all the latest updates. I am using the latest NVIDIA drivers. I’ve tried every option in the Multi-Display/Mixed GPU Acceleration options; they’re all equally bad performance-wise (but again only in OpenGL).