The issue with selecting and placing displays always requires more precision than is generally applied in the back-and-forth we have in various fora. That's because there's an interaction between the pixel density per inch (PPI), the total number of pixels (resolution is 3840x2160 for 4k), the screen size, the viewing distance, viewing height, and finally any magnification factors you'd apply to the native resolution that reduce it in a disciplined way.
I have an article on my website called '4k Hooray' that walks through those factors and has multiple web links to calculation sites. The predecessor to that article was 'The 4k in the Road', and it journaled my frustration with the transition from HD (1920x1200) displays and a WHD (2560x1600) display.
Right now, I usually run my 55-inch 4k at 115% magnification in Win10, and at the first notch below native (can't remember the numbers) in macOS. It's enough to make my eyes happy without much sacrifices in 'screen real estate' . My viewing distance is around 42 inches.
For example, a 50-inch display from 10 years ago was probably still just HD (1920x1080) and so there was no real estate advantage over a smaller display, but there was the advantage of a longer viewing distance. In my 55-inch implementation, I had to sacrifice a convenient viewing height because of my mixer, but gained the advantages of more screen real estate by laying out my track, console, and video windows in a different manner than before.
Don't give up. It's possible to get what you want with patience, a tape measure and some calculations.