I had that motherboard and had the same issue with the CPU speed reporting incorrectly like yours.
I believe windows reports the speed by checking your front side bus speed and multipies by the
stock multiplier. If you up the bus speed but lower the multiplier it doesn't catch the lowered multiplier therefore giving a higher speed than you are actually running.
I killed that board by flashing the bios with what turned out to be a bad processor installed, may it rest in peace.
