I realize this reply is late, but i too very quickly noticed my gpu's temp skyrocket pretty fast. Im not sure what is causing it but i know a fair amount of older/indie games dont tend to work well with the newer monitors. My fps was showing at between 4k/6k which is obviously way above the fps norm. Thi was in windows mode.

However, a simple fix to this is downloading/using MSI afterburner. Put you gcard's fan to 80% speed and it should solve the issue, its a great peice of free software ad free and 100% trustable. I use it all the time to see what games cause my gcard to heat up to scary lvls and then adjust fan speed as needed. (Im well aware some video game companies say this and other software like it can interfear with games, but i have yet to experience gcard fan software of anykind making a game unable to work).

Choose to necro bump/reply when i couldint find much on the subject regarding vsync either in hopes this helps some people.