I started monitoring a Phenom II X6 core frequency. It seems that the Cool'n'Quiet drops
to 2400->1600->800 MHz. I even saw half the cores running at 1600 MHz and the others at
only 800 MHz. This is despite the fact that I was only loading 1 core of 6. There is no way
the thing should be overheating.

I do not see what is the problem, please elaborate. Is not CnQ doing what it is supposed to?
You can also set power options to High Performance and then run e.g nuclearusmc as a test.

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As I understand turbo-boost, if only one CPU is thrashed, it will be boosted, and three idle CPUs will drop to 800 MHz. I have not seen any boost, only
falls in core frequency. It seems to me that the active CPU is the one dropping to 800 MHz, the thing is so slow.
I also think it should not overheat with only one CPU at 100% usage. I once hit reset and went to health monitor in BIOS.
The temperature was under 60 Celcius. So I am wondering if my mainboard has a bug sending wrong signals to the X6.

What is your motherboard? Have you updated to latest BIOS version? I assume you are referring to AMD's Turbo Core technology?

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