I believe 800 MHz is the speed it is supposed to run at when it is in its lowest power management state.
First of all, have you noticed an ACTUAL drop in performance in REAL applications, or are you just going by what AMD Overdrive and 3DMark are reporting? It is quite possible that they are merely reporting what the CPU is running at AT THAT TIME; if the system is very lightly loaded, then it is quite possible that it really is running at only 800 MHz when the tool is checking the clock speed.
I'm a little surprised that disabling CnQ made no difference.
Try running something to put some load on the CPU cores and see if AMD Overdrive and/or 3DMark still report 800 MHz.
Do you have the latest BIOS for that board installed?
Have you tried resetting the CMOS?
Nostalgia isn't what it used to be.