Some boards, such as the ASUS A8N SLI-Premium will let you overclock/overvolt and still use Cool n' Quiet. I kind of found this by accident on my own board. I was trying to see how high I could overclock my system without having to disable CnQ and once I pushed the BIOS FSB above 210mhz, I noticed it would apply an extra 0.15v at all times.
In other words, it would idle at 1.25v (rather than 1.1v) and the 5x CPU multiplier, then under heavy load shoot up to 1.50v and the 11x multiplier. I have a 3700+ SanDiego 2.2ghz, by the way. Anyway, by dropping the memory multiplier down I was able to clock all the way up to a 250mhz FSB, which is 25% o/c and 2.75ghz, 15-minute Prime95 stable (didn't bother running longer than that since it was just a test out of curiosity) and still have CnQ enabled.
It's hillarious to have an A64 that will do 2.75ghz and still drop back to 1.25ghz @ 1.25v when you're not stressing it. I used CrystalCPUID on my old computer and it seems like the BIOS/Windows implementation of CnQ responds faster than I was ever able to make crystal respond. For that reason, I would try to use the BIOS implementation whenever possible.
The great part for myself was that I found out that my x2 3800+ runs at stock speeds and 1.15v dual prime95 stable (1.15v is the lowest voltage that I can give with CrystalCPUID, since I am limited by the cnq voltages options + asus gives an extra 0.05V on everything
) . So now under load it will run at 2.0ghz and 1.15v instead of 1.35v like it did with cnq. My bios gives no voltage options for user, so CCPUID is the only way for me to undervolt. Too bad I cannot go lower then 1.15v
. CrystalCPUID has the options, but my motherboard is setting me back on this. With a better board my cpu could probably run at 1.0v @ 1.0ghz or maybe even lower voltage.