Thanks.. just to let everyone know. I am on 2009 Mac Pro ,4.1 flash to 5.1.. I was already on high sierra 10.13.6 boot rom
MP51.0085.B00. I downloaded the full installer, ran it, it said i needed to update firmware, did the shutdown, held the power button until it flashed, let go, then a beep, machine updated firmware but could not see anything on the screen, it rebooted back into OSX, installer was still open and ready to continue, checked boot rom and it updated to 138.0.0.0.0.
( so for me it updated from MP51.0085.B00 to 138.0.0.0.0.) no issue; but I was already on 10.13.6.
Installed running now. I will report back. My card was already flashed from the person i bought it from for any future updates. You can test your card by downloading the metal benchmark app form the app store. if it runs then you know it is metal compatible already.
[doublepost=1537836132][/doublepost]
A mentioned above my card is - AMD radeon R9 280x. Installer is running now with 33 min left. I will report back once done. (i see the apple logo at boot as well)
all done