When you turn on EIST
(Speedstep) of Intel CPUs, CPU clock speed varies on system loads. For example, Core i7 920 allows multiplier to be changed from x12 to x22 (when Turbo boost is turn on). The default clock multiplier is x20. So, the clock speed can vary 1.6GHz to 2.67HZ, and, by TurboBoost, it can be up to 2.9GHz.
However, if the system is woken up from sleep/hibernation, CPU clock is just stuck x20, i.e., steedstep is not working anymore. But, the machine itself works smoothly. I need to reboot the machine to enable EIST again.
I'm not sure this is the problem of MB/CPU or Windows 7. But, I never experienced with Windows Vista. Is there anyone who have similar problem? If you're using EIST and sleep/hibernation frequently, please check your system.
The clock speed and multiplier can be easily checked by CPU-Z