You won't get to 4GHz stable on that board, the 3 phase VRM is going to hate running a quad at a decent overclock even if they're decent quality phases.
I know it's too late saying it now but instead of buying watercooling you should have bought a board that can handle a quad at high clockspeeds and an air cooler.
That said, set memory 1:1 with your FSB (so 666/7MHz at 3GHz if you're on the 9x multi) then up the FSB slowly until you encounter instability. When you encounter instability try increasing either the NB voltage or your CPU Vcore to stabilise your overclock.
Go easy on the Vcore because a 3 phase VRM means it won't handle the extra current that will be flowing through the CPU at higher OCs well at all, put a fan over the heatsink to the left of your CPU socket and if it's getting too hot back down. Personally, I'd leave it, a 3 phase VRM is not enough to overclock a Q6600 to the fullest.
Sorry to be the bearer of bad news but I would strongly recommend against going above 3 on that board, if you want to try anyway just be very conservative with voltage.
Edit: Mods like this one
exist because the VRM is insufficient for an overclocked quad, there should be some info on that page if you're wondering why a 3 phase VRM might cause a problem.
Edit2: And I'm not suggesting you mod it, I know I'd screw up a mod like that if I tried it. I'm just saying a mod like that wouldn't be necessary if the board didn't have serious problems with quads.
's an example of someone who pushed his Vcore too far and killed something with a P5KC and Q6600. (page 3 for the bit where he says it's dead)Edited by Mike-IRL - 5/15/12 at 5:32am