I can`t help it
You need to consider a few things here, I think.
- Resolution --> the number of pixels that are displayed on a screen
- Screen size --> the physical size of the panel (the space to put the pixels on so to speak)
So, a screen size of 27 inch that is filled with 1920x1280/1200/1080 pixels is what we are used to more or less.
A very comfortable relation between the number of pixels and the size of the panel.
Working with a monitor like that is easy on the eyes (provided the panels picture quality is good).
Two 27 inch monitors is still a very good way of working.
Now, if you fill the same screen (27 inch) with UHD 16:9 with 3840x2160px (NOT 4k (which is 4096x2160px) like it is wrongly titulated)
you can imagine that the text and/or icons displayed on that screen will look small, a lot smaller!
And no: "all information spread over more pixels" is not happening here - when the size of the screen/panel stays the same (in this case 27 inch).
More and more OSes and programs let you counter this by scaling up your content on screen.
You can imagine that a larger monitor is better suited for a large number of pixels.
The next thing is the "native resolution" of a given panel.
As I said earlier, changing this requires software or the gpu to interpolate between pixels.
So the picture quality will suffer depending on how good the algorithms are.
Scaling down is what would happen in case of a native "4k" resolution monitor to HD sized content.
Picture quality after that process can differ a lot...
You can get a feel for what is happening when you change your display settings to a much smaller resolution:
set it to 1680x1050 for example. The (virtual) desktop size gets smaller - displayed content gets larger.
This is the same effect as when you change from 4k to 1920x1200 pixels on the 27 inch monitor.
Some pics:
just remember that you need to "re-project" the Full HD resolution to the area occupied by the Ultra HD resolution in the picture.
This represents your (new) monitors native resolution (UHD) and the screen size (27 inch).
To look at Full HD (1920x1080px) the content needs to be up-scaled to that screen size
and the number of pixel is "reduced" (more pixels show the same picture element).
See above - how well this is done by software inside the monitor is the thing that makes a good screen.
I hope this helps a little and does not sound to patronizing (Oberschullehrerhaft)
And of course, sorry, if you have read or know all that already...and hopefully I did not make any mistakes
CHeers, Klaus