Just a quick positive user report.
I cloned my win 10 boot drive, a 500gb SSD in bay 3, to an image, and then restored it to a 1TB SSD in bay 4. The machine would not boot successfully. After reading around in these forums I began to suspect that if I moved the newly-cloned drive to bay 3 it would work.
Success! This saved a real pile of hassle in wresting with Brigadier and Apple’s Boot Camp releases since the classic Mac Pros are officially unsupported and the current release of Boot Camp places significant restrictions on the user’s ability to install Windows on a separate physical volume.
Hope this note clarifies things for other cMP users out there!