I think 27" 4K is better then 24", for computer use. I have a good 2.5K and I don't see any pixelisation (but the scripts/icons are very tiny).
Please note that computer screens are not used like television screens: we are nearer to the screen as we should be to watch movies: We move the head to read menus, windows, etc. (especially with big screen or multiple screens), but this allow us to use information quicker than to switch windows. To watch movies, we must allow some more distance, and get most of the screen without moving our head, so if you watch a lot of movies and you cannot sit some foot behind, a 24" should be better.
Personally, I would not yet but a 4K: not so high quality (or very expensive). OLED are also not so long-lasting (8h per day every day). We are still waiting the promised "better pixels" (which are slowly coming to TV), so better colors (like the original UHD specifications) more bit depth (also in original UHD specification), more static contrast [and these reference monitors are very very expensive]. And BTW I prefer multiple monitors.