that's how it works you get thermal throttling or power throttling
if you look [google] you can see some guys showin there 900 cards throttle as low as 60-64c then you got to look at NVidia gpu boost [gpu boost 2.0 for a 900 series] all this is set in the cards bios
this is why for the 900 cards a water block or hybrid was in demand and hard to get / find some models did not even get one made for it like by EK
I got a 980 ti hybrid never see thermal throttling with it seeing my card at highest max temps are only 48c average at full load 45c
also at 85c is about where you will see throttling
http://forums.evga.com/980-Ti-Downclocking-Above-60C-m2355251.aspx
https://forums.geforce.com/default/topic/841761/gtx-980-ti-temp-question/
http://www.overclock.net/t/1561166/gtx-980-ti-throttles-at-65-degrees
gpu boost 2.0
http://www.anandtech.com/show/6760/nvidias-geforce-gtx-titan-part-1/5
https://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_Titan/30.html
http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/61310-nvidia-geforce-gtx-780-review-3.html
a of course good old luck of the draw comes in to play on how each card will handle all that