Your MB has NB over temp protection that shuts it off should the NB go over the chosen setting. I believe options are 70, 80, & 90c. In the BIOS it's under Power, Hardware Monitor, NB Overheat Protection. You need to know NB voltages with everything set at auto, (no overclock) as a starting point. Mine runs at 1.36v stock and I've raised it to 1.5v, though it will trip the NB temp protection if it's set on 70c fairly quickly under load at that voltage. I'd say you're pretty safe with temp protection set on 70c, if you're raising voltages in small stages, and you're monitoring temps under load with Prime95 or similar. Idle temps are really meaningless as when the system loads to 100% temps rise sharply.