Well I managed to achieve 4.25Ghz (500Mhz fsb) for a 50% overclock on air cooling.
It took a lot of voltage to make it stable in OCCT though (over 1.37v) so I backed it down to 4Ghz at 1.35v for normal usage. A 40% overclock is definitely not bad though
My temps are pretty good and as long as I leave the memory at 942Mhz (rather than 1130Mhz using the next highest ratio) it seems to be perfectly stable. The memory is still at 5-5-5-15 at 1.9v too, so it runs nice and cool.
I'm happy though. This setup should be pretty freaking fast for quite a long time. My next upgrade will definitely be a graphics card, and I think this board and CPU will be more than enough to push Fermi or a 5870 X2 if I'm feeling rich in a few months.