If you go 4K then you want to have 27" or above !
Not necessarily for what I will mainly be working with.
My new 'work' desk will have 2 monitors. My current Dell u29 superwide which is 2560x1080 and my new, lets say for sake of argument, 24 inch 4k screen - the NEC MultiSync EA244UHD (currently my hot favourite to buy).
I use Lightroom 90% of the time for my photography work, only dipping out into Photoshop CS6 for critical stuff. In lightroom I can have the grid view of thumnailed images and menus on the Dell 1080p, nice and easy to read, but nice and wide to display many. If I set lightroom to Loupe view then the thumbnail you click on opens up full screen on your second monitor - which in this case would be the 24 inch 4k. So I'll get full screen super DPI res to work on each image properly. At that resolution/DPI and physical size, in
theory the clarity is sooooooo good and sharp, it should be like working on an A3+/ even bigger print in front of your face, which is no doubt amazing.
Also, in terms of form factor, on a smallish desk in a smallish home office, a 24 inch screen at about 1.5 to 2 feet from you is fine and plenty big enough no?
Also, far as I understand it windows 10, which I will be upgrading to when it's all set up, allows for independent scaling of monitors.
i.e. you can do this for each monitor on your desktop, independently of one another:
So I could set the 24 inch 4k to 150% for example, and leave the other screen as is. Therefore it *should* be great to have one 4k 24 inch, and one 2560 x 1080 screen as a working 2 screen desktop, and a photo/ video editing platform. In fact I've read a few articles that suggest it's good to have a 1080p screen alongside ANY 4k screen when editing photos, so you can proof on both types of display ie you need to remember most people won't be viewing your images on a 4k scrren.
Also, tied to this, the NEC 24" 4k has full Adobe RGB/ wide colour gamut factory calibrated mode. It also has sRGB factory calibrated mode, that you can physically switch between. However I think it will be much more use friendly to simply slide a window over to the 1080p sRGB dell to quickly and easily check and proof images.
I'm rambling now, good night.