Bizarre processor speed issue in HP m7260n Media Center PC

I have recently purchased two Hewlett-Packard m7260n Media Center PCs. In
exploring the systems, I discovered one very strange thing related to
processor speed, and it perplexes me.

These PCs use Intel's dual-core Pentium D CPU, running at 3.0 GHz. However,
when I open the System Properties - General tab on the machines, one reports
the processor speed, correctly, as 3.0 GHz. The other reports the processor
speed, incorrectly, as 2.79 GHz. I've run a number of tests on the "2.79"
PC, using - variously - the Intel Processor ID Utility, Performance Test 6.0
(shareware), and even Microsoft's System Information utility. ALL of these
tools (and HP's own supplied diagnostic tools) - as well as the BIOS -
correctly report the machine as having a Pentium D 3.0 GHz processor.

Does anyone have an idea why - given that apparently the correct processor
is installed - one machine would report itself as having the incorrect
processor? I've contacted HP about this with, predictably, uninformative
results.

Thanks for any help anyone can give in shedding light on this issue.