I had to make this very choice for my new workstation this summer and I went with 40" 16:9 4K (Dell 4317PQ iirc) because I wanted the vertical space. It's "retina" when sitting about 80cm away which is fine for that size, and I can have 3 apps side-by-side no problem (usually terminals + some IDE in my case). I love this display. I think the way forward is to break the ratio limitations, all of them, by moving towards gigantic dispays.