This is a fantastic spreadsheet Home Theatre Calculator: Viewing Distance, Screen Size.

It allows you to enter things like resolution, screen size, visual acuity, seating distances, lumens etc. and gives various comments on brightness of image and whether the resolution is visible.

In my room, 4K will be visible from my seating distance but that's it, which is great, because I can finally stop upgrading at 4K. No need for anything higher...

My Music : My Cinema