I use one as my main monitor, it's very good. Every time I upgrade my monitor size, it's irreversible since the claustrophobia of using a smaller display increases.
What viewing distance do you use?
Jumping in here, but I use a 55" curved 4k Samsung as a monitor (per recommendation of my optometrist). I stand around 40" from the center of the screen.
Did the optometrist say why that size and curvature specifically?
No, that was more me playing around with what would work (I started with a 4k 42" Seiki TV and this was the upgrade. At sizes larger than 40" the curved screen really helps you with better seeing the corners of the screen without having to lean.
It varies a bit between sitting and standing, but about 100 cm to the closest point. To the furthest corner it's another 20 cm.
Unfortunately it seems there are no longer any OLED computer monitors on the market, with Dell having discontinued theirs. So if you want such a display you're forced to buy a smart TV (disregarding very expensive professional reference monitors).
This is actually what I ended up settling on for my personal space. But I would still like something bigger for a group viewing scenario (i.e. living room).