I used dual monitors since Win95B enabled it back in the mid 90’s. I did not use a mac until probably 2008 or so.
At any rate, while in the past I was a strong advocate of dual monitors, I much prefer my 40" TV in my office. A couple years ago one of my 27" monitors running 2560x1440 died, and I had to either get a replacement 27" or single 40" TV. There was a sale at the time where I got the TV for only like $20USD more than a replacement 2560x1440 27".
And the TV’s energy savings compared to the 27 inch “energy saver” would actually pay for the TV within a year. I’ll never look back. For my purposes, the 40" is better in every way. I often treat is as two side by side 1920 x 2160 monitors with zero bezel between them. And have hotkeys assigned to via Better Touch Tool to instantly move / resize a window to various areas of my 3840x2160 workspace. Less total pixel width than my previous dual 2560 width, but for development purposes I prefer the 50% greater height because I can see so more more at once vertically by the time you lose some top area to toolbars, lower area to search / debug panes, etc. And there is still plenty of horizontal width to show all the windows and floating palettes I want.
At the time I went with 40" instead of 43" even though they were very nearly the same price, because the 40" worked out to nearly exactly the same pixels per inch as my previous 27" monitors. A 50" was barely more money too, but would require more head movement to take in, and I calculated that at my viewing distance, I would be better off with the 40". It’s been great.
I can see where needing bifocals or split glasses or whatever you want to call them could present a serious impediment. So YMMV. But I absolutely love it.
When traveling, I now use a 16" MBP with dual 4k external 15.6" monitors, but all
running a lower resolution than 4k because my aging eyes cannot comfortably read at a 4k resolution anymore. I will second the recommendation for SwitchResX to gain more control over available resolutions, and setup multiple display groups you can hop between via hot keys. Great for resizing for different configurations to see what a window would look like at various user resolutions.
Personally, I consider 4K to be 1080p equivalent, since ideal scale is 200%. Sure, you can pick other resolutions, but they either won’t be pixel-perfect, or really small. But I suppose 4K at 40” isn’t any different than 1080p at 20” when both are set to 100% scale.