Re: Speedstep ?
When you have modern CPU, core logic, and operating system you should only have Enhanced Speedstep or Speedstep enabled. C1E, the halt state, should be disabled in this case when these are used. If your operating system is the latter, what does not support Speedstep, then you use C1E and disable Speedstep. The latter would be before Windows XP.
To note with Asus motherboards ACPI (2.0) is often disabled and should be enabled.