>Quad-Core 2.6GHz Intel Xeon Broadwell E5-2623 v4 [4-cores / 8-threads]
We are well into Skylake era, a Broadwell is ancient comparatively speaking. The Mac Pro will be Cascade Lake, not state of the Art like EPYC with 7nm. But still a very large improvement.
>HP Z Turbo Drive Even if we choose a 256GB version of Z Turbo instead of SATA as you confined, the Turbo Drive will still be a lot slower.
>HP Thunderbolt 2 (20GB/s; one port) +$200 Yes, Thunderbolt Port are expensive. And these are only TB2, not even TB3, and still missing 3 Port.
>Intel X540-T2 | Dual-Port | RJ45 | PCIe 2.0 | 10GbE Network Adapter
Even this 2013 Dual Port 10Gbps Ethernet is a $250 upgrade.
>Wireless Mouse and Keyboard, and WiFi Added those .
So a not similar config with a very old Intel CPU cost $3475. I would imagine if you spec it exactly the same as Mac Pro, with TB3 and every hardware and ports, the HP would cost $4K+, with an ugly design. Quite a bit of saving but not as dramatic as some would imagine.
I tried coming up with something similar to the base spec MacPro but got larger storage, more cores and an Nvidia card with a decent saving.