4k screen is rather a strange one, as size alters a lot, as you can get a 4k screen at 23,8in at 2560x1440 Resolution
but which may not look as good as a 27in at 1920x1080 Resolution for many reasons, the panel, how the screen has been made and designed etc
Contrast Ratio Brightness Response Time Analogue Input DVI-D Input HDMI Input Year On-Site Warranty.
i use a 32" 1920X1080 IPS WIDESCREEN LED MONITOR plus a 40" 1920X1080 VA FREESYNC CURVED WIDESCREEN LCD and 5 others ranging from 29" to 22" and laptops for testing with 14 and 17" screens.
2 different tech's, LED and LCD
but other parts are different as well, the price, the response times, the contrast ration etc and the list goes on.
LCDs allow displays to be much thinner than cathode ray tube (CRT) technology. This is because an LED TV uses light-emitting diodes for back lighting as opposed to the CCFLs of conventional LCD TVs. While in LCD fluorescent lights in an LCD TVs are always behind the screen.
so which one is better? that's a wallet call and depends on your budget, larger is always better than smaller, faster response time is always better than slower, in FPS anyway,...
so to confuse you even more, what do you use now? etc tech and size, and are you going bigger in screen size or just in resolution?
as i've known many people who went from a 27 or 29" monitor to a same size just to get a higher resolution find out it wasn't worth the effort for what they got, so look first and ask yourself, what games do i play, and how many support it?
eg: so if your like me who uses 1920x1080 in 1 or 2 sizes, 32" and 40" and then goto a 27 or 29" just to get 2560x1440 Resolution or bigger 2560X1080 or 3440x1440 or 3840X2160
then expect some serious draw backs unless you pay top end and don't get one with slower or lower Contrast Ratio Brightness Response Time less Analogue Input less DVI-D Input less HDMI Input and a 1 Year On-Site Warranty only.
but hopefully someone will post a 4k screen shot and host it somewhere for you, as the best shot will be too large to host here i'd guess