That will be normal after 15mins of continuous use of furmark. VDDC will throttle down at 120c or 125c. But I would not recommend running at those temps for long if at all, unless you want to kill your card. (Furmark is a big GPU killer!!) You should not get VDDC above 75c whilst gaming for a couple of hours. If you do, then either your waterblock is not fitted properly/your loop is small (RAD size and pump speed) or your card can't take the overclock. Cheers, Simon.