I have an EFI flashed Radeon HD 7970. The EFI supports standard monitor sizes like the 27" Cinema display, but it cannot deal with the larger sizes supported by the card.
I now have a Dell UW38 display running 3840x1600 and do not have a display until the regular driver loads. Oddly, the BIOS display for BootCamp is ok. But it makes it impossible to use the built-in boot manager (option key down.)
Does BootRunner have its own driver or does it use the EFI driver? Is the driver capable of handling 384x1600 displays?