These are some of the high end monitors that are out now with that 2560x1440 resolution and as you can see in looking at the spec's they all have 5 -7ms response time. I had a 27" 1920x1080 Lg that had a 2ms respnse time and went to a 30" HP 2560x1600 and 7ms response time and did not notice any difference in gaming. Depending on your gaming skill set you may or may not see any difference.
These new 27" monitors also have some new features like;
Wide Quad High Definition
Delivering four times the pixel resolution of HD, the 27-inch ASUS PB278Q is a 2560 by 1440 Wide Quad High Definition (WQHD) monitor that brings incredible definition to your games, videos, and everything else you do.
The PLS panel provides an ultra-wide 178-degree viewing angle and a superior matrice design compared to other panels for enhanced definition and detail.