Every time something like this comes out, someone like you posts what you did.
I am 40 years old, my eyes aren't special in any way.
I sit 3 feet from a trio of Dell 30" monitors at 2560x1600 and I can see the pixels. Playing games, you have to turn on the AA or the jaggies are crazy.
I sit 10 feet from a Sony 70" 1080p TV, and I can see the pixels. Doesn't matter the content, they are there. Of course, when relaxing and watching a movie, you just ignore them after awhile, but they are there.
At 10 feet, a 70" 4k screen is just about perfect. I can kinda, sorta, almost see the pixels, just... as I age, I'm sure I won't be able to.
I haven't upgraded to a 4k screen because there is nothing to watch at that resolution, and it appears that will be the case for some time.
I do plan to upgrade my EyeFinity setup on my desk to a trio of 32" 4K IPS displays sometime soon, but that also will probably be all I need since my eyes will get worse over time.
I can see the value in 8k screens for some applications, but I suspect we're largely done at that point for anything within reason.