There's no doubt Apple's 5K iMacs are fabulous machines. I've had the pleasure to use the 2017 model for about two weeks now and it's by far the best computing device I have ever used.
Of course the main selling point is the 27", 5K resolution, DCI-P3 color space display. In case you want to
brag about it in front of your friends compare its resolution to other common display resolutions, I made a simple diagram.
The image is 5120x2880, so if you download it and display it in fullscreen mode on an iMac you get a better impression of it.