Had that same thing happen, but only when not using nice round numbers.
When i use 425x8, it shows 425x8 in cpuz
i think when at something like 378x8 , it showed 377x8 in cpuz
I don't really have an exact answer, but i did set the ram timings manually, added +.1 to
the fsb, mch, pcie
Maybe that won't do anything as i don't see why it would make it show 425 instead of 424.
Perhaps a bios update might help.
Also the voltage difference is that this board has vdroop under load
Actually, i believe most if not all P35 boards have vdroop