Hello, I have a 2010 Mac Pro with the stock ATI Radeon 5770. When I boot with a 20" DVI Cinema Display attached, everything works perfectly , I get drive selection if I boot holding option, and I can see the password field to disable FileVault 2. Where my issue arises is that my normal setup is two Dell U2715H displays plugged in through Mini DisplayPort (not using MST). Even just connecting one U2715H alone via Mini DisplayPort causes the Mac to display no video until midway through the boot into an macOS partition. Is the lack of EFI display an expected behaviour of the 5770 when connected to a MDP display? Or is there a way I can cause the Mac Pro to display video whilst booting with a 5770 and MDP display(s). Thanks!