There is no reason to disable speedstep unless it's causing instability.
It only slows down when you're not using it.
Once it's under load e.g. a game or Prime95 etc, it jumps to it's top speed.
Don't disable power saving features if you're system is stable. It will not give you a performance increase because they are only ever active when you're barely using your system.
As above, if you want to see the full speed values, download and run the Prime 95 torture test in the background while looking at CPU-Z. Your CPU will automatically jump to full speed as soon as it's asked to do something.