Increasing the CPU clock:
The result is quite good, but Kentsfield is like a little reactor: it gets hot very easily even when it's idling, so hardcore overclockers need to use water-cooling or other similar methods to keep the CPU cool. It would be possible to squeeze some more MHz out of our CPU but we stayed on the conservative side, so our result was "only" 3750MHz, which is still quite nice.
The Penryn, on the other hand, is a very cool customer. You can go up to 1.6000V VCore and it will not hurt it, which is quite amazing. We could go up to 4300MHz and did some tests, but we did not check if this configuration was prime stable. For our benching we decided to use a common frequency of 4GHz.