At 4k resolution, a 30-40 inch monitor gives noticeably improved text quality (even when I could only get it at 30hz). Part of the reason for this is that we're looking at the screen from 2.5-3 feet away, rather than the ~6ft viewing distance that is common for TVs.

It's hard to describe the difference, except that I have two monitors side by side -- one a 4k, and one a 1440p, and the difference is noticeable. Even when I scale the 4k monitor so that the window size is the same, the text quality is still noticeably easier to read.

For web app development my setup is as follows:

4k monitor for two panes of code

4k monitor for a browser + debugger or maybe two browsers: one mobile one desktop.

1080p monitor for docs or maybe Netflix as I work depending on the kind of work.

When I'm doing robotics or server or more general programming work I basically just use my main monitor.

Reading code on a 1080p monitor is almost intolerable now that I'm used to 4k. I can size it way down and get two full panes of code side by side.

OLED is not back lit, so it probably looks better than plasma once you account for the higher pixel density. I haven’t done a side by side comparison though.

It's as natural and balanced as you want it to be. I recently watched "The Revenant" in 4k HDR on an LG Oled Panel, the movie was apparently filmed only with natural light (not in the way you meant, just that there was no artificial lighting for scenes). It's absolutely stunning to see as everything feels spot on.

OLED is not the same thing as what they advertise as LED, which is really LED backlit LCD. OLED screens have no backlighting, and so when properly tuned, the picture is 100% perfect. I'm with you though, I love my plasma TV from 2009 and don't plan to give it up any time soon.

HDR alone will make your plasma look old. I went from a plasma to 4k then to hdr. Huge improvement.

The difference in resolution from 1080p is very noticeable and a definite improvement if you prefer more detail in your movies.