Add AppleCare for iMac because its all-in-one design may not be as robust as the Mac Pro, and because parts like the display backlighting are very expensive to fix. AppleCare covers things for a total of 3 years, versus one year for factory warranty.
The late 2015 iMac 5K remains as impressive as ever on the performance front, but the 5K display is really what impresses as an unrivalled image presentation device without peer for color imagery and for black and white imagery. See iMac 5K: Building a High-Performance Configuration. The image below is a screen shot, but what cannot be communicated on any other display is the sheer richness of the blacks, the outstanding contrast, and of course the fine details (see more on that in my photography blog).