2 cores stuck at low clock frequency?

Starting to throttle now :S

Closed the game I was playing and the throttling stopped, went back to 4GHz..

Disabled turbo and it's at 3.7GHz atm - hasn't throttled with the game I play yet.

AMD overdrive reports thermal margin readings of around 27c - is this OK?

Also cooler is an Artic Alpine GT 64 Rev.2

Noticed that clock speeds throttle down to 1.7GHz on max CPU load (100% on all cores). I tried a sony vegas render attempt and clock speeds are occasionally throttling down to 1.7GHz then up again.

Is there a way to stop this?