I decided to try Vantage with my CPU @ 3.2GHz to see how much FPS I'd lose in the graphics test.
There's Vantage on my rig @ 3.2GHz.
My other score is in the above post.
Keep in mind we're talking about a 1280x res with no filtering and Tri-SLi. Ignore the score and look at FPS in GPU test 1 and 2.
Test 1 = 71.11FPS vs 79.93FPS
Test 2 = 75.46FPS vs 80.6FPS
Obviously @ 1920x those differences would be much smaller. So it looks like even a 3.2GHz 920 is fairly solid support for well overclocked GTX 260 Tri-SLi.
There's the Vantage GPU score with extreme quality settings with my CPU @ 3.2GHz. GPU score is 14479.