I connected my ASUS PB278Q to my laptop running Ubuntu 16.05.1 LTS and discovered it wouldn't run at 2560x1440. For some reason, Linux doesn't discover the maximum resolution of this monitor. I discovered this article:

Cannot establish maximum resolution on ASUS PB278Q

I is a simple fix. Basically, run cvt with the correct options and add a modeline to ~/.xprofile. Here's the excerpt from the page which works perfectly:

$ cvt -v 2560 1440 40

2560x1440 39.96 Hz (CVT) hsync: 58.98 kHz; pclk: 201.00 MHz
 Modeline "2560x1440_40.00" 201.00 2560 2720 2984 3408 1440 1443 1448 1476 -hsync +vsync

$ xrandr --newmode "2560x1440_40.00" 201.00 2560 2720 2984 3408 1440 1443 1448 1476 -hsync +vsync

$ xrandr --addmode HDMI1 "2560x1440_40.00"