My issue with 4K gaming is a purely numerological one.
1440p has 1.78x the pixels of 1080p
4K has 2.25x the pixels of 1440p
So the bump to 1440p is good but the bump from that to 4K is larger, for a smaller benefit. Now that seems unfair, why should that be a smaller benefit?
IMO the benefit of 4K isn't there yet because there's no additional geometry advantage. I play at 1440p and I see the geometry limitations all the time, so while I could get higher resolution texture rendering at 4K, the geometry is identical so it looks no more realistic. Distance viewing will be better at 4K but I don't find that the kind of distance viewing which takes advantage of the increased rez is something that I use in-game.
Actually if someone could post a game suggestion which makes effective use of high rez distance elements, that would be great (especially if I own it...).
I recently downgraded my rez from 34" 3440x1440 to 32" 2560x1440 to get 144Hz and was concerned that the reduction in rez (as I play zoomed out to match the screen width with some additional height) would be noticeable and it's simply not in-game, thanks to limitations in geometry.