I currently use a LG 29UM67-P. This monitor has a refresh rate of 75. With the DX9 client, I am able to play the game in fullscreen at 75 FPS.
With the DX11 client, the Frame Rate Limit is set to 75 fps (Refresh Rate 1/1) but my FPS goes to a max of 60. The same applies if I play in Borderless Windowed. If I select Windowed, my FPS will go back up to 75.
If I turn off the Frame Rate Limit in Full Screen, I will get 75 FPS but a lot of tearing.