I have just upgraded the monitor connected to my late 2013 15" rMBP. I was using a 24" 1920x1200 CCFL-backlit HP ZR24w. I have just bought a 27" 2560x1440 flicker-free LED-backlit Acer B276HUL to replace it. The same mini-DisplayPort to DisplayPort cable has been used for each monitor. Image quality on the new 27" monitor is awful. It looks like the image is being scaled or processed aggressively. Text is particularly bad. Stroke width varies from almost disappearing to blocky, often with a halo. Settings for the monitor is set to "Default for display". Changing to Scaled shows that 2560 x 1440 is selected. A screen grab produces an image of the correct resolution (and shows no problems when viewed on the laptop display). The monitor has a "Wide mode" menu option which I have set to "1:1", but have also tried "Full" and "Aspect". The "DP" setting is set to "DP 1.2", but have tried "DP 1.1". Does anyone have any suggestions please?