4k monitor

I connect my MacBook pro to 2 x LG Ultrafine monitors, one 21" and the other 27". LR Classic works fine.  In LR CC I can see no way of having the same interface as Classic, i.e. LR in one monitor and the currently selected photo full screen on the other. Maybe I am missing something? (You can of course mirror the displays and this works, but to serve what purpose other than teaching etc. I cannot see, certainly no use for editing).

They are of course working with 4K monitors.
The menues and interfaces are properly sized.
But be aware that using a 4K monitor needs much more detailed previews and computer power. This can cause frustratingly slow reaction times.
(See in this threads in comments of many 4K users:
https://feedback.photoshop.com/photos... and
https://feedback.photoshop.com/photos... )
I am also facing some issues of incorrectly displayed cursors ( https://feedback.photoshop.com/photos... )

In my experience Lightroom is OK but Photoshop is challenging as the fonts are really really small and not sized properly.  Perhaps Arnold knows something I don't about how to get the menus properly sized.  

I work with a 32" Philips 4k monitor.
Its works file in Lightroom CC, less zoom in and more space for usefull menus

I use a 27" 5k iMac und would call the font size in Lightroom Classic and Photoshop tiny but more or less readable (UI fonts set to "large" in both programs). When you are experienced with both programs, it's useable. When you are a newby, perhaps you will spend some time hanging over your desk with your head close to the monitor trying to read the labels. 

Depending on from which monitor resolution you are upgrading, give yourself some time to get used to the 4k. In the first couple of weeks everythings seems a little bit to small.

If you are using Windows, you should have a look at the release notes of the latest Photoshop version. Adobe made a big fuss about the latest release of Photoshop now supporting hi-res monitors with Windows10.

Thank’s a lot for your comments. I think I'll not buy a 4K monitor. Not now.
 

I use Photoshop CC 2018 and Lightroom Classic CC with a 27" 5K Retina iMac ( screen resolution 219 pixels per inch ( 5120 pixels / 23.375 inches ) or 84.87 ppcm) and a 27" 4K benQ SW271 (screen resolution ( 3840 (pixels) / 23.375 (inches) = 164 ppi or 65 PpCM).

I have no issues with either program on either display. 

Let your photo dealer know that since te doesn't think it is a good match for Photoshop or Lightroom  that he should give you a discount on that 4K Eizo.

my menus in lr CC are small in 4k monitors...did you have to do anything to size them up?

I use a 40'' Samsung TV with 4k resolution calibrated to 99% sRGB.
I have the windows Custom Display Scaling set to 150% and I do sit about 1m away from the screen.

This way the menus are quite good readable.

Photoshop is good, too.

In former times Adobe did not take notice of the setting in Windows (like font-size and scaling), but since CC 2018 (or 2015.7 ?) they do - now the menus are a big as in other applications.

My MacBook Pro 15,6'' 2016 does work with this display well, too - but due to the weaker graphics card it's a little slow when using a 4k resolution, so I do work with the Windows machine (where I have a Nvidia 1050 ti installed).