Late 2015 Apple iMac 5K: a Display Without Peer for Sheer Viewing Pleasure
See iMac 5K: Building a High-Performance Configuration as well as Photography / Videography: Enhancing your iMac 5K (or Mac Pro).
Get the new iMac 5K at B&H Photo (thanks for using MPG link). MPG computer gear wishlist.
I (Lloyd) have been using the late 2015 iMac 5K for some months as an adjunct to the 2013 Mac Pro for intensive photography work.
Specifically the late 2015 iMac 5K Retina with 4.0 GHz Intel Core i7 (Skylake), 1TB Flash, 8GB memory, AMD Radeon R9 M395X GPU (4GB GDDR5) with 64GB OWC memory.
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).