Cpu multiplier is not constant

http://en.wikipedia.org/wiki/SpeedStep

It's called speedstep. Keeps power usage down when PC's not strained. It doesn't need turning off unless causing problems or overclocking.

In your BIOS, find an option for EIST and disable it.

http://ark.intel.com/Product.aspx?id=36463

That would be intel speed step at work. this feature aloud the cpu to clock down when there little activity going on. Benefit of this are:

Cool cpu = overall cooler case
Low power consumption

Now when you start running most apps (like games) your cpu will run at stock speeds.

So there no need to turn this feature off.

True. The usual procedure is to turn it off while you are working out overclock settings, then turn it back on afterward if you wish.

I always turn it back on.