Bios setting is either called C state or C1E, by disabling this your multiplier will lock at your custom setting, I prefer not to do this, so you get best of both worlds, power saving & performance when needed.
The technology is refered to as SpeedStep. It drops your clock rate down to 1.6 when the cpu is being lightly used to save power, then ramps it up to your designated clock rating when the cpu begins to work harder.
So yes, when your playing a game the cpu should speedstep up to 4ghz. You can disable this in the BIOS. Go to the advanced BIOS, then the Advanced tab. Under the Advanced Tab there should be CPU configuration, then under the new screen you get to from choosing that option, scroll down to CPU Power Management, the speedstep enable/disable will be in the new window onces CPU PM is selected: http://www.legitreviews.com/images/reviews/1767/asus-p9...
Tell me man do you like the Sabertooth Z77..My Motherboard died so im building a new rig and im in the middle of waiting for all the parts i ordered and i bought the Sabertooth Z77...I hear the ivy Bridge blows so i picked up the 2600k... with 8 gb/s of corsair Vengeance 1866 and i cant wait to see the performance of my 2 OCZ vertex 3 in raid 0..I hear the board feature i controle dont work worth a dam so i not going to install it...Do you think you can pass me some of your knowledge about the board i hear the latest bios don't work so well...One guy installed it and all his pcie x1 slots stopped working...Im sure this board still has a few bugs till they get the right bios set up im sure there will be problems.