AMD's Cool n' Quiet is the equality of Intel's SpeedStep so I could tell you that you should disable it. It's just not worth it.
If you are overclocking your not looking to save energy, are you? If you overclock you CPU to 3.8Ghz, why are you going to run it at 1Ghz when your browsing the web. There is also a time delay when the processor speeds up, but as far as I know, that only hampers the Phenom Family as it has a bugged up Cn'Q 2.0(Not Phenom II). If your CPU keeps changing from 1Ghz or so all the way to a higher speed, and in this case a very high speed, I would think it would take a longer time to speed up.
No idea if you could understand much of that because I'm mostly tired as hell right now, but if you want a vote from me, I say disable it.