What is it that you do that requires 4k? Genuinely curious. I'm a software engineer and to me 4k sounds like it wouldn't make a difference. But maybe you are one too and I just don't know any better. Thanks in advance.
I can view ~6 open files at once (more depending), and this can be very helpful when trying to remember context: instead of remembering, I just split the screen and open the same file again.
When I got a 4K monitor, it replaced my previous dual monitor setup. I now prefer just one high-res monitor. Only disadvantage is that I spend time tweaking font sizes, but that's mostly front-loaded and once it's set up (Linux) I don't even think about it.