PC Games Hardware did some tests on how much gaming performance on a GeForce GTX 280 system is affected by the performance of the processor. You can check it out over here.
In our detailed benchmark analysis the Geforce GTX 280 runs with a 3.6 GHz Dore 2 Duo (Wolfdale core). The following review will reveal why this is a reasonable decision and how much the GT200 addicted to the CPU power. To achieve this we set our E8500 (6 MiByte L2-Cache) to clock speeds between 2 and 4 GHz. All tests were made at a resolution of 1.680x1.050 with 4x FSAA and 16:1 AF.
One of the games that clearly illustrates the importance of a good CPU is Crysis. In the test the average FPS didn't really change but there were huge gains in the minimum FPS as the processor clock went higher. Another nice example is World in Conflict, in this game the minimum FPS increased from 16 FPS at 3GHz to 23 FPS at 4GHz.