I have a 2008 Mac Pro 3,1. Without actually paying attention (or caring) I bought an XFX Radeon HD 6670 off of eBay a few years ago. I currently have three OSs on three seperate hard drives (El capitan, high Sierra, Windows 10). Because I’m contatantly switching boot drives, it would be extremely helpful to see the boot screen. I have scoured Google to no avail. Does anyone have any advice or now how to flash an HD 6670 to work with an efi?