It's the processor revision - the "G0" revision of the Q6600 overclocks amazingly - you're pretty much guaranteed to exceed 3.0GHz. Mine's at 3.2GHz, with at least another 400MHz in reserve.

I think all Q6600 Pros are the latest revision.

If you're not sure, download CPU-Z, which will tell you:



What sort of clock speed is the 8800GT btw?