Apparently performance is off the charts...
"Off the charts" in the sense that it's so far below the dual socket workstations with the same chip that it's invisible?
Whatever Apple does, HP/Dell/Lenovo/SuperMicro... can double or triple it with dual CPU sockets and quad GPUs.
That's what an expandable box gives you.
I could be talked into a Mac Pro based on price and specs. But it has to be less then $3K including monitor and SSD!
Perhaps with a 17" monitor and a 32 GB SSD, quad core 16 GiB and single GPU with 512 MiB VRAM.