I've had the pleasure of owning and shooting some of the PWS MK. series of rifles and i can't say enough good about them. To my understanding the Pro series is the same operating system with out some of the "fancy" creature comforts.
Currently running a Mk111 Pro for work. Love it other than the added weight. They claim barrel and bcg are same as the other line but idk. Compared mine side by side with a Mk111 Mod 2 each set up with Eotech, Dbal and similar lights and the pro is much heavier. It shoots tight groups though, the bolt doesn’t get dirty, and I can afford it on a cops salary with three kids.
I don’t own one. When I held one I thought the upper looked different. It is 6061 Aluminium. From what I could see is there was a little more tooling marks and the anodizing looked different than the lower. I’m sure it’s an awesome setup though.