The GTX 980ti is well capable of playing games at 1440p at about 100fps or more depending on the game settings. As well as this the GPU is G-Sync capable and so is the monitor so games should look great. I wouldn't have any concerns and should be perfect for playing games at 1440p. Also display ports to my knowledge are the only ports capable of G-Sync so you should choose the display port over a HDMI port.
-Mitch