I am using a 28" 4k samsung at work and bought myself the Asus PB287Q I'm not so bothered by the lack of IPS panel at least in the standard or sRGB display modes the colour reproduction looks good, only if I change it into game mode does it look absolutely appalling. I've yet to do any development at home on it but most things tend to look fine at the viewing distance in Windows, occasionally need to zoom webpages. It's not as easy on the eyes at work possibly because I'm running it through HDMI (laptop without display port) so only 30hz and the stand on the Samsung is fixed pointing up and it sits further away from me on my desk, I regularly get comments like "how on earth can you read that".

Just an update, after some careful consideration I decided that 4k was too much for my eyes and instead with a 27" 2560x1440 display. I brought in the monitor to work to see how a full day of development goes using one large screen resolution and so far so good. I will report back by the end of my work day and let you know my initial reaction and whether it caused me any eye strain or I feel like my productivity increased or decreased.

And here I was hoping this would be a thread about writing 4k demos...

I had a long day today 11 hours in fact, but I'm here to report that it felt real good having one 2560x1440 monitor. It felt like I had 2 monitors even tho it was only one, I was able to snap the windows in different locations and not have to switch between docked applications much. My eyes feel good, not strained at all and I feel like I definitely made a good decision in getting the display.

I think physical DPI (e.g. your eyesight/eye-strain) and DPI scaling issues are the primary concerns. I use a 30" 2560x1600 as my primary display at work and at home (in both cases flanked by 1200x1600 (portrait) displays of identical height/DPI on both sides), and I don't think I could go much higher DPI comfortably -- Maybe 3K would be doable, but not more -- or if 5K were a viable thing I might be tempted to use one with UI DPI scaling at 200% and just take the sharper text/images.

There's a 37" or 42" inexpensive 4K television that some people were touting at a computer display. It only runs at 30Hz though, so its no go for graphics. It might make an interesting setup if you used that display for doing work, and then paired it with a nice 1080p, low-latency gaming display for testing/gaming -- you could put the 1080 display above the 4k if footprint is a concern.

And another option would be a 34" ultrawide 3440x1440 monitor, like this one. Dpi ought not be a problem, and you get a little more real estate.

Seems like you might've made your choice already, but just sharing for those who are following.

I've tried working with single large monitors, but I generally go back to a multi-monitor setup rather quickly. For one I just find it far easier on the eyes in the long term when I'm moving back and forth between different focus points, so I keep my monitors at slightly different distances.

I tend to go for a single 'large' monitor in my setups as the main central screen, and then flank it with a smaller cheaper monitor, ideally a matched pair on either side, and with the option to rotate them between portrait and landscape modes.

Another update, I can't go back to 1080p as this is my first day of full work without the monitor :-\