I currently play in 4k 60hz, WoW, Rise of the tomb raider, The Witcher 3, GTA 5, Farcry Primal, Total War Warhammer, Elite Dangerous, and a few others.
Games I play at 1440p 165hz are, Battlefield 1, Space Hulk Deathwing, The Division, Metro Last Light and a few other fast paced games.