What resolution are you gaming at? CPU bottlenecks are also influenced by resolution. A CPU that bottlenecks a GPU at 1280 x 1024 (17" CRT or 19" LCD native resolution, though some 19" LCD are 1440 x 900), might not be a bottleneck at 1680 x 1050 (22" LCD).
Using a higher resolution allows the GPU more headroom. The GPU cranks out fewer fps, but the CPU can often handle it, so the actual fps you get go up a bit.