According to this calculator, my 65" 4k setup is around 100ppd.

I find that anything more than that (e.g. sitting further away, or replacing it with an 8k screen of same size) requires scaling up text and wasting a lot of pixels when rendering other things.

So yeah, I think 8k is a total waste if you’re not targeting a much higher fov, at which point a curved screen would probably be better.