Apple doesn't seem too interested in updating the Mac Pro. I already have three monitors I'm quite happy with, so I'm hesitant to buy a computer with a monitor built in — which significantly hurts the IMac's chances for me. Still, despite updating my video card and such, my mid 2010 8-core Mac Pro is getting pretty long in the tooth.
I've been looking at puget systems.:
https://www.pugetsystems.com who actually work with you to build a custom machine based on how you're looking to use it.
Sure, it's PC, but everything I've found online has given them pretty high marks (I've been hemming and hawing about taking the leap for over a year now). I continue to read up on Windows 10 and continue to be torn.