On the low end ($2,350ish):
1. Case: Fractal Design XL R2 Black Silent $137
2. PSU: EVGA SuperNOVA 750 G+ $110
3. Motherboard: ASUS Pro WS X570-Ace $370
4. CPU: Ryzen 9 3900 (12 core/24 thread) $450ish
5. Memory: Crucial 32GB DDR4 3200 ECC (Each) $720 - (4 sticks for 128Gb)
6. Video: RX 5700 $350
7. SSD: Corsair Force MP600 (500Gb) $140
So, what do we have here?
1. Quiet Case - added bonus - no RGB
2. A PSU with more than enough grunt, because the CPU doesn't require a 1K PSU. And no RGB.
3. A motherboard that will use ECC ram - added bonus - no RGB.
4. A 65 watt CPU with 50% more cores/threads than a base Mac Pro - No RGB.
5. 4 times the ECC ram of a base Mac Pro. All AMD CPUs will use ECC if the motherboard supports it. And no RGB
6. A Navi based CPU - no proprietary connector, no last generation (or later GPU) for me. And no RGB
7. PCIe 4.0 hard drive, faster and twice the size of a Base Mac Pro. And no RGB.
8. And I can buy this right now......
9. If you don't want to build it yourself, you can order it (albeit with a case with a side window and liquid cooling) from VelocityMicro.com for a shade over $2,800.
10. Added bonus - an AM4 socket motherboard means I can drop in a Zen3 CPU in 2020. I don't see that happening with Intel's "Socket of the Month" strategy.
You can do the same thing with a threadripper system - it will start at about $3,500 to match the base Mac Pro (8 cores/32Gb ram/RX 580). At $6,500 you are at 32 cores & 256Gb of ram.
Eypc will start at about $4,500 and can go to a 128 core system for $31,000 or thereabouts.
The price/performance ratio will get even worse if Intel follows through and lowers the price of their CPUs across the board, because we know Timmy won't do that.