I am having the exact same problem as this poster. I am running a GTX 970 with the Dell provided display port cable to my S2716DG. The monitor is only a few days old so I can still return/exchange if necessary. I already tried the recommendation of the clean install for the latest Nvidia graphics driver 385.69. I do not see an actual resolution on that thread? Thank you for your assistance.
Are you saying that the S2716DG flickers when set to 2560x1440 60Hz? According to Nvidia, the September 2014 GTX 970 is not qualified to do higher Hz (G-Sync) because it does not have the required 586MHz pixel clock.