It is at this point you pop off the heatsink, unscrew the heat spreader, then clean off the thermal compound to look at the markings on the CPU. You would also check the multiplier settings at this point. A WS/PDQ overclocking page should be pretty clear on the multiplier setting.

Was it the PDQ or Lombard that unscrewed? I forget. IIRC on one the heat spreader unscrewed and on the other it just popped out but I do not remember any further details.

I might be mixing this up with a different model completely.

Anyway, remember to apply fresh thermal compound to replace whatever was removed and do not mangle the thermal pad on the heatsink.