Apologies in advance for the lengthy post, I'm trying to be thorough in the hopes someone here can help me fix this before I go mad. My hardware setup is a Mac Pro 4,1->5,1 running Sierra 10.12.6 on a PCIe SSD and Windows 10 on a second PCIe SSD, with a 1080ti. I have no issues installing and setting up Windows 10, or using the 1080ti in either OS with the proper NVidia drivers. The issue I am experiencing is that after setting up Windows 10, once I boot into macOS I lose the ability to get back into Windows easily. Startup Disk shows both macOS and Windows volumes, but selecting and booting into the Windows volume results in a black screen with "No bootable device found". After this point, the only way back into macOS is via Recovery or the boot device manager, either of which requires that I clear the NVRAM and swap out the 1080ti for the original GT120 in order to access the boot screens. While in the boot device manager, I have an additional option for "EFI Boot", which if selected will successfully boot into Windows...once. What I want, is to be able to set up both OSes and switch between them without needing Recovery or the boot device manager, so I can throw the GT120 in a desk drawer and never worry about boot screens again. I have thought of a few ways this might be doable, but I can't get any of them figured out and am desperate for assistance - a bottle of scotch to the first person who can get me where I want to go! So, my questions are: 1. Is there any way to manually add the "EFI Boot" option to the Startup Disk preferences pane, so I can select it directly from within macOS to boot straight into Windows, and then use Boot Camp Configuration to boot back into macOS from Windows? OR 2. Is there a way to programmatically tell macOS to boot to the "EFI Boot" option via a script or from the Terminal, to achieve the same result in a less-graceful manner? OR 3. Is there a way to manually configure the boot setup on the Windows volume so that it can be booted directly without the need for "EFI Boot"? OR 4. Can anybody flash an EVGA 1080ti SC2, so I can avoid this entire situation forever? Many thanks in advance for any input!