Just to give you an idea, I run a single 1440p on overclocked 970s in SLI (each 970 is within 92% or so performance of a 980). Witcher 3 runs an average in the 70s, dipping down below 60FPS on occasion (Hairworks off). On the other end of the spectrum Star Wars Battlefront and Grid Autosport run 120-130FPS. Other games fall in the middle of those extremes between 70s and 120+, like FC4, Crysis 3, and Project Cars. This is with all game settings maxed and ultra with 4xAA (sometimes FXAA in Nvidia control panel for games that support it + 2xMSAA).
With that said, since my monitor is only overclocked to 80Hz, I run V-sync on in the games. This is exactly where a nice Gsync monitor would come in handy to be able to use those extra FPS between the different games.