I’m lost… I have the same problem: Windowed borderless is capped at 60 FPS
I just had to reinstall the computer due to a corrupted windows, so it’s the SAME machine it worked on before (nevertheless I had trouble setting it up the first time, until I found the vsync = off tip) …not this time though 
My setup is a dual monitor with an LG Ultragear which runs on 144Hz and an older Monitor which runs on 60 Hz, both definately set in the Nvidia system control settings. I also turned off the Vsync there ( in the 3D Settings) and turned G-sync for windowed and full screen.
I tried every setting in Overwatch I read about here, without success. vsync, Custom Frame rate, different Resolutions, restart the game multiple times. I even tried lower quality setting… 60 FPS in borderless, that’s it. Fullframe is working, but thats no option if you want to watch a Movie while waiting for a game 
help me Obiwan Kenobi…
cheers
Michael
edit: In the end…a bloody system reboot did it! … argh!