These are very nice cards - 4 outputs only 1 PCI-EX power connector. So we might have 8 monitors inside Mac Pro, but it's not working well. I've flashed HIS iCooler HD7770 1 GB GDDR5 card and it seems card is properly working but I cannot get output on any of ports. This is how it looks like: http://www.newegg.com/Product/Product.aspx?Item=N82E16814161402 So I've added a working HD5770 in slot 1 and HD7770 in slot 3. All booted fine and it seems it sees a VGA monitor even if nothing is connected to the card. I'm attaching my original ROM and EFI rom for diagnosis. It seems card is properly working with 5.0 GT/s ! Does anyone have any success with HD7770 inside Mac Pro ?