Here are some articles you can read to understand how this works:
We regularly have folks coming here complaining that they never see the highest clock speed. Folks don't seem to understand that the highest rate is only going to be achieved in those rare cases where only a single Core is active (and hence the reason why I always start by pointing people to these papers). They think that running a heavy-duty benchmark test of some sort should cause this maximum to happen, but this is actually the worst-case scenario! The test will make *all* of the Cores busy and this flat out stops Turbo from ever being activated. Bottom line, you should see the boosting occurring and higher clock rates being achieved, but it is rare to see the highest rate occurring.