So I have a GTX 670 and a mac pro 1,1 that I've flash to be a 2,1. I currently have a 8800gt in it and it's pretty decent in el capitan in terms of os performance but I would still like to upgrade to the 670 so it could perform better in games. Thing is I have two os x installations (10.11.6 and 10.7.5) as well as ubuntu and windows 10 on the same computer. So I really need the boot screen so I can see which hard drive I'm booting from. Is there anyway to flash it to make it work, I've done lots of research and from what I've read since apple never made mac pro compatible gtx 670's there's pretty much no compatible EFI bios on the internet to just download and flash with nvflash.