Also it can depend on what your power properties are set to. On mine for a while cpu-z would always show mine at 21x multi no matter what it was actually at. Also the actual multi would bounce around a lot when idle. I found the solution was to (using XP) change the power properties from desktop to portable/laptop. That allowed it to have a stable 12x at idle and 21x at load and cpu-z started to finally report the correct multi.
Here is a shot showing what it looked like with cpu-z reporting the incorrect multi.
And here is a shot of what I changed to correct the problem.
And same was true in W7 RC but had quite a few more options to set but I started with power saver mode and changed from there.