Jack: Yes I see what you mean. This is just like two threads running in parallel and all stuff about FSB, memory, hypertransport is the CPU management (CPU work).
But that also means that the frame rate isn't good for testing how smooth the game is. It's just frames that may be a bit old because how "up to date" the picture is depends on when the cpu did its work for it.
If the CPU decides frame rate speed and it is above 30 to 40 FPS and LOW FPS is above 25 then the game will be smooth. But if the game has an average 60 FPS and it is the GPU that slows the game to that frame rate the game could in fact behave more unresponsive and delayed compared to when the slower frame rate decided by the cpu.