TweakTown overclocked the G0 SLACR Q6600 to 4GHz:

There we have it, the Q6600 G0, and it clearly lives up to the hype. The Q6600 sits at about the same price as the E6850 and we have a quad-core chip at 2.4GHz or a dual-core at 3GHz. The decision on which one to buy was hard, the real problem now though is that with the release of the SLACR G0 Q6600s the decision is that much harder again.

We would probably recommend the Q6600, if you get 3.3GHz out of it it's going to kill in games, but you also have the advantage of four cores; and while a lot of games might not be using it at the moment there are a number of applications that do, so on the whole it's probably the better choice.

From personal experience I have just moved from an E6600 which ran at stock (yuck! But it's used for work) to a Q6600, again not overclocked. Slightly skeptical on the effect it was going to have on my overall computer experience (in the sense was I going to notice the difference between four cores @ 2.4GHz vs two cores @ 2.4GHz) I figured there was only one way to find out. What I have noticed is that over the past few weeks I can do little things like leave my Adobe Photoshop CS3 open for days on end, or be alt-tabbing between a game of Civilization 4 which takes me four days to complete. Saving and exiting games is so dual-core!

If you've got an E6600 and want something a bit more productive look at the Q6600. If you're looking for a new CPU and tossing up between an E6850 or Q6600, go the quad-core, at least you can also tell your friends you have a quad-core, that sounds more impressive than dual! We love the Q6600 and so should you, no doubt it's going to keep all those enthusiasts happy until AMD release the Phenom and Intel their new Penryn.