So...after years of waiting for even a hint that a high-performance Mac desktop sans monitor was coming, I threw in the towel. I built an i6700K/32GB/ASUS mATx/SSD (multi)/GTX 950 hackintosh. I hadn't built a machine since my pre-Apple days in the late 1990s. I figured if my hackintosh build was unsuccessful, I would cringe and go over to the dark side. Fortunately, I now have a "gold build" in Sierra 10.12.3 with everything (USB, Audio, Video, iMessage, etc) functioning perfectly -- I was very surprised! It took about 10 hours of construction, install and debug time.
Lightroom and Photoshop are my heavy uses (42 megapixel RAW images). I was getting by with a late 2014 27" Retina i5 iMac with fusion drive. I was pretty shocked by the performance delta:
(late 2014 i5 iMac vs i7 Hackintosh):
Geekbench 4: 11,250 vs 17,400 (before overclocking)
Cinebench 15 Rendering: 85 fps vs 116 fps (with a budget placeholder video card)
Import 10 RAWs to LR and convert to DNG: 58s vs 15s (!)
Export 10 full sized JPGs from RAWs: 74s vs 33s (!)
I was amazed by the Lightroom difference. I'm sure the SSD helped a bit, but the rendering times are amazingly better. I suspect the Nvidia GTX card helps a lot more than the AMD m290x, but I may do some more testing on that front. I double checked all of my settings as well. Anyway, all I know is it's a lot faster and that's very helpful.
I have no illusions that this will require a fair bit of maintenance, but I'm very comfortable with that. And....I have lots of backups!