The Maximum operating temperatures for different GPUS are as follows:
GTX 700 Series
780/780Ti/Titan/Titan Black - 95C
770 - 98C
760 - 97C
GTX 500/600 Series - 97C
GTX 200/400 Series - 105C
Temperatures in excess of these are considered unsafe, and your system may shut down to protect itself from heat-related damage.