WMI not reporting CPU speed correctly

We audit our machines with a vbs script & WMI. All is well except that on certain PCs WMI reports an unrealistically high processor speed – 2400MHz on a 1GHz CPU etc…
I’m using the win32_processor class with the MaxProcessorSpeed value.
TechNetsays that there’s a problem reporting CPU Name on certain types of processor (it returns Unknown processor Pentium 6) but says nothing about the wrong clock speeds.

Any help will be gratefully welcomed.

JP