My own pair of classic MacPros are set up in a similar way. I find it a very impressive and flexible setup indeed.
I have the MacPros running the current BigSur, and they can multi-boot to 10.15, 10.14, 10.6, and 10.5. The more powerful system also boots into Windows10, where the new FlightSim 2020 rules. I run Parallels in one of the installations, and have all the systems 10.5 to 11.3 installed that way, (and WIndows 95, 98, 2000, and Ubuntu 2020.04). VirtualBox runs Tiger Intel and i386 Snow Leopard. I’m sure Apple must look at my App Store profile and wonder what the heck is going on... Ken
