Run Prime95 torture test. Guaranteed you'll get all those cores running at 3.6GHz (assuming your cooling is sufficient). At loads of less than 100%, the cpu will assume it can go faster on a few cores, as faster = better. As long as the cpu temps are not in throttle ranges, the cores will go as fast as they can, which in your case is 4.1GHz.
This is a benefit. There's not all that many games or even programs that will max out 6c/12t usage, they'll generally use 4c/8t at most, so bumping speeds with PBO gets higher performance on fewer cores.