So, I have a iMac with i5 Quad Core, and it seems like there is some kind of clock problems. I do play games on this machine, but the problem is iMac starts to change to clock in some point and it makes games to lag. It changes to 2.8 (or other numbers), then 2.66, and so on. Like Battlefield Bad Company 2, game runs very well (60fps~) on 720P Medium setting, and about 10 minutes later it starts to change the clocks. So it runs 20fps for few seconds, then 60~, and so on. This continues even on low setting on the graphics. I check the temperatures, and it was lower than 65C at CPU. This is very irritating especially when I am recording, because it goes to 10~15 fps when it happens. I tried to disable turbo boost and make a clock stay at 2.66 no matter what, but still I did not solved this. I even tried power management menu on Windows 7. It did not work on 'High Performance'. I found on that if you change the full CPU speed on 75% in that menu sometimes it stays on the same clock speed. But it performs little slower. Any ideas? Maybe just an heating control of Apple?