So I built my rig a few months ago and I have a GTX 660 in it. The Gigabyte one with 3gb of VRAM instead of the factory 2. I love it but now that I've gotten super into parts and performance I'd like to overclock it. I'm thinking of using EVGA precision X. How long should I stress test my gpu for (will be using valley)? And what should I be doing to get the best overclock? Turn my power target all the way up and just go for it? All the guides I've seen are very vague about power target and what an acceptable amount of extra voltage is.