modern intel chips have a technology known as EIST - normally shortened to 'speedstep
' - which basically slows the chip down when it isn't being used heavily. this also cranks down the voltage, thus saving power and reducing heat buildup. this is a Good Thing.
if you try starting a program which uses the processor (eg a virus scan), you should notice that your processor will then start running at its top speed.
so, try running a virus scan and check cpu-z again - it should then report your overclocked speed.