I don't think an equivalent PC really costs $7000 USD....
A Dell Precision 7000 will set you back US$3000 at a configuration similar to the iMac Pro. Add a good 27" 5K display, PCI-based SSD and you are close to US$ 6000 with a GPU that's a generation behind. And it comes with Windows. Nobody deserves that.
I'm sure with $4700 more it's possible to get something still better than this new imac pro.. yet with a good cooling system and upgradable at any time.
edit: $2300 INCLUDING 15% taxes