980ti with water cooler mod. I'm able to run it with a pretty nasty overclock, and since it no longer heat throttles, I'm getting near GTX 1080 performance, which is why I decided to hold off and wait for 1080ti instead. All my screenshots I'm getting very playable fps.
However I did do an experiment with Tomb Raider, where you run the game at 5K (nvidia supersampling mode) and the game unlocks additional graphics on the face, like better shine and detail. Although its not playable for me (only 20fps). Maybe the additional graphics are meant for future cards that laugh at 5K