This will be a short list, to keep things focused—consult with Lloyd for specific needs/concerns, including not just performance but color management and displays, data safety including fault tolerance and when to use or not use RAID, and backup.
Regrettably, 8K is not yet here for computers, at least not Macs. That will have to wait for 2018/2019, both for graphics card and bus support, but also affordable external 8K displays.
Existing recommendation — 2013 Mac Pro
That recommendation remains solid with a stronger justification as ever—more so as time has proven. For example, Lloyd’s 2013 Mac Pro has been off AppleCare for 6 months, but has been a stalwart performer for over 3.6 years now.
There are terrific deals on the gear to build a 2013 Mac Pro photography system. Items below form the core of that system.
New pending recommendation: 2017 iMac 5K or iMac Pro
“Pending” because there remain unanswered questions: iMac Pro performance and pricing, the vaporware new Mac Pro, and sea change to a Thunderbolt 3 / USB-C world of peripherals.
The new Mac Pro can be dismissed out of hand, because Apple has provided so little information on timing of release and features that no planning can be done— teaser 2 years in advance is just worthless for any planning under a year ahead. The promised new Mac Pro should ignored for anyone needing a new system within the next 6 months, at least.
Second, it remains to be seen whether the 2017 iMac Pro can prove performance benefits over a much less expensive and very speedy 2017 iMac 5K. MPG intends to answer that question just as soon as the 2017 iMac Pro is announced with pricing and specifications, and one that can be obtained and tested. Disappointing that Apple did not release an iMac Pro 8K or at least 6K. See also Will the iMac Pro Be Worth The Cost?.
That leaves the nearly 4-year recommendation for the 2013 Mac Pro, or the 4-core but very speedy 2017 iMac 5K. Based on performance and pricing and Thunderbolt 3 support and that lovely 5K display with its included free computer, MPG deems the 2017 iMac 5K a slightly better choice for photographers buying now, though professionals will need to add a wide gamut calibrated display to do things right. There may be exceptions for edge cases, but 6 weeks of field use with the slower 2015 Apple iMac 5K prove out these statements.
For nearly 4 years, the MPG recommendation for a high performance photography setup has been a 6-core 2013 Mac Pro with 64GB memory, 1TB SSD, and OWC Thunderbay 4. There are terrific deals on all that gear right today as this is being written and that recommendation remains solid with strong justification as ever—years of usage that should be problem-free.
The 2017 iMac 5K to be purchased is model APIMTRMNED44, about $3699 at BHPhoto.com. To that, items from the following list should be added, with suitably size backup drives for the choice of main storage
There is one caveat: MPG has been told that Thunderbolt 3 versions of the Thunderbay 4 are coming very soon—buyers should wait on that, which means it would behoove buyers to wait for the MPG tests between the iMac Pro and the 2017 iMac 5K. By the time those results are known, Thunderbolt 3 storage should be shipping or about to ship.