You will have to contact HP, not sure if they will give you the information, but you can tell them what you have found out with CPU-Z, and you have concerns about the voltage that is listed and also core speed and multiplier.
I work for a HP Channel Partner and I know that monitoring software doesnt always read HP motherboards correctly. I wouild try some other software first.
for example there is HWinfo
http://www.hwinfo.com/
that is freeware and a program I use every day.
just need to pick between 32 bit and 64 bit depending on your OS
if your not sure check your C drive
if you have only one program folder then you have 32 bit
if you have two programs folders then you have 64bit