Hi! Before doing the installation, I took some informations. The title seems as a scoop, but you can actually find plenty of sites telling that Windows 10 is not compatible with Mac Pro 5.1, as the Apple support page (swiss-french, but you can turn it to en-us): https://support.apple.com/fr-ch/HT204990 . First explanation offered on some of the sites: "Microsoft were about not to support Mac Pro 5.1 Intel processors anymore". Well, a machine (in which I invested nowadays for third the price), which in 2013 costed about USD 15000.-, and even 17000.- with a Nvidia Quadro K5000 Mac, were about to be not anymore supported by Microsoft? Windows 8 were the only Microsoft OS we could install on it, when older PCs are compatible? I could not believe it. I followed the explained procedure you can find here: http://forums.macrumors.com/threads/better-than-bootcamp-guide.1858662/#post-22922590 as far I had an additional barrier: the PCIe configuration of the SSD. But, yes, I also took other precautions: I let the Mac OS 10.9.5 without additional update and even less upgrade, and did the same with Windows 8.1 Pro eligible to 10, after what I updated Windows 8.1 to 10. I am now doing the Mac OS X upgrade to X.11.5. I can guarantee you that Microsoft Windows 10 support the Mac Pro 5.1 configuration; this is Apple, who want to sell half configured Mac Pro "6".1 (which accept half the RAM and SSD at max), based on AMD graphic cards, in case of any Windows 10 restriction about 5.1.