I was thinking about getting a 4k display for photo and video editing. I just edit 1080p video and that was never a problem on my mid 2012 mbp non-retina with i5 and 8gb ram. It also was never a problem when I had a external 1080p display hooked up to it with a thunderbolt to hdmi adapter. Can the macbook run a 4k display even for basic tasks like web browsing and some stuff in sketch and affinity designer?
According to Everymac that machine can only run an external screen up to 2560x1600.
I run a 2012 non Retina MBP El Capitan and use a Moshi TB to HDMI adapter to run my Samsung 4K 40" TV at 4K. The only problem is sometimes it is finicky reconnecting after putting the Mac in sleep mode or turning off the TV power. I have to plug/unplug the cables several times.
However it is a great setup with lots of desktop room which is great when I work with music in Sibelius. I can see a big chunk of the score at once and I can magnify web pages, word docs, etc. so I can see the print much more easily.
4K at a foot away!