Are you sure you turned off EVERYTHING? SpeedStep and C-States, in particular?
Regardless, you should leave those ENABLED anyway. There's literally NO reason not to.
You DON'T need full speed ALL the time. I leave all of that enabled, even with my 4.5 OC because having a solid 4.5 ALL the time is pointless. Low idle speed and voltage is a GOOD thing.
Edit: Wow, this one got EVERYBODY to reply, lol.