I'd love the 4k for productivity; the 34" ultrawides are so tempting, but this running 21:9 is possible, so its hard to buy an ultrawide.
This is what I'm considering as well. Think of how much code you can fit on a 40" 4k screen!
if a game can't run on ultra I can try the snazzy 21:9 aspect ratio or use it as an excuse to buy me another card.