My experience is with "Good Cooling", the Q6600 will safely OC 3.5Ghz so long as you don't exceed voltage 1.45v. If it won't hold a stable OC above that voltage, leave it alone. 3.6Ghz is relatively stable but causes some instability at times under stress, so not worth it. 3.7Ghz will boot and run but usually error out under stress after a short time without upping voltages beyond reasonable limits, again, not worth it.