So, I was playing around with my BIOS settings trying to tweak things, when I noticed my brain somehow had completely omitted the CPU cache ratio.
I hade previously loaded some XMP setting, but it used a 125Mhz BCKL which I subsequently changed to 100Mhz. That, in turn, put the cache ratio at 24. Pretty darn low, I should say. And I've been running with those settings for a long time...

Well, can't complain when I suddenly find that there's some untapped performance to be gained.

Anyhow, started to increase the cache ratio incrementally, until...

When I put the cache ratio close to the core ratio the wrong clock speed is reported in POST. 43x101Mhz is reported as a clock speed of 4242Mhz in POST. CPUID reports the correct clock speed of 4343Mhz.

Any idea why it's doing that?