I have a 65 (4K/HDR) size TV and I sit 3.15m from it.
I have connected PS4 Pro and 1080Ti PC to it, so I play 4k often.
But before (1 year ago) I had a 55 inches 1080p TV.
I do not feel much difference. Really.
That 55 inches TV I have moved to other room and I lie 2.6m from it.
Connected to it other PC, PS3, X360. 1080p still feels great.