First off, there is no pre set "This Vcore for This Clock", each chip is different and will need a different vcore to attain a specific clock. Best way it to start from stock and work your way up until you are no longer stable, and give it a step of vcore. I recommend prime95 for stability testing, you will want to run it each time you clock higher, and let it run for at least 30minutes, if any of the threads fail before 30-45minutes, you will need to give it one more bump on vcore. And hopefully you are using a good cooler, as the quads put out a good amount of heat, the stock heatsink wont cut it for overclocking.