how much can i OC my Q6600 stock cooler..rampage formula

Overclock until your core temperature reaches 65-70 at the max, but IME, the q6600 runs a bit hot, and I don't mind taking it up to 65-70. Some will say to stay below 55, but that would mean you probably wouldn't want to bump your vcore up much, if at all. You'd hit 3.0ghz easy, just raise your FSB from 266 to 333, and ta-dah!
 
With the stock cooler you could reach 3.0 GHz, and depending on the temperature of the computer room and the case ventilation probably even less before you encounter high temp problems at full load, the Q6600 runs really hot.