I wondered if my Q6600 had a FSB wall around 452 MHz. I had cut the heatpipe away between NB and PWM heatsinks, so NB sink was burning hot. I had an urge to install a waterblock there, and that is what I did. It was a bit tricky operation, because the naked die.
I managed to get everything working though.

Check rest of the pics: Checking contact between IHS and Swiftech Apogee and adding NB block - Flickr

My MCH voltage is now 1.65V and I could boot FSB @ 450 MHz.
CPU VTT is 1.425V

On average, where is Q6600s FSB wall around?