Those are pretty normal temperature ranges for the 780 Ti.
Which model of the 780 Ti do you have? If it's EVGA or ASUS, they tend to have software you can set a more aggressive fan profile for if you want to keep the card cooler, but this comes at a cost of the fan getting louder.
GPU Boost 2.0 works on temperature, so the software sets a temperature target, then goes to 100%, and spins up the fans as fast as it needs to in order to stay at 100% at that temperature target. You can generally use software like ASUS's GPU monitoring utility or EVGA Precision X to set the temperature target manually.