An overclock as such, has nothing to do with the OS, overclocking is the same process as what happens to a stock cpu on boot, just faster. The OS loads later. That said, there are parts of the OS that can affect an OS, such as windows power settings, sleep settings etc as those will override any bios settings, thereby screwing up the OC. But realistically you don't need an OS at all to OC, it's just handy to have one for tedting/stability purposes.