Flashed or not it will beahave like a PC one in 1,1/2,1 = no bootscreen. These Macs are unable to load 64bit-only EFI and use only PC part of the ROM.
I met these problems today. I wanted to use an 8800GTS flahed as 8800GT/EFI in a MacPro4,1 but in vain.
Also GT120 doesn't run in MacPro2,1 with Tiamo efi boot file.
So i stay with cards as it was...
Apple and EFI, tss tss..