I have an Early 2009 MP that was a 4,1 but had been flashed to a 5,1 when I replaced the original procs w/2 x 3.33 GHz 6-cores. Am trying to figure out if I'm going to screw up my system if I upgrade to Sierra. Originally I found this: http://create.pro/blog/macos-sierra-tested-working-200920102012-mac-pro-51-good-go-apples-latest-os/ Which seemed to give an all clear. But then I also ran into this which was written a day later: http://www.macnn.com/articles/16/06...ems.for.the.aluminum.mac.pro.faithful.134675/ Which seems to say that there are critical issues w/PCI-e expansion cards. Which would be problematic for me since I have two slotted in, a HighPoint RocketU 4-Port USB 3.0 and another one which just gives me a single eSata port. And I guess my AMD Radeon HD 7950 if that counts. Has anyone else out there w/a 5,1 that has PCI-e cards installed upgraded to Sierra yet? Any issues?