So, the other thread with the list of compatibility issues says the 5870 works on the two 1,1 undocumented Boot Roms, but still isn't booting on the MP11.005C.B08. I just ordered this card, so I'm a bit nervous now. Has there really been any more information on this?
Here's the other thread: https://forums.macrumors.com/threads/1002692/
If it doesn't work you can always return it, just say that you didn't notice it was only for the 2009/2010 rev's and only noticed that when you started reading the instructions manuals. Just be sure to not scratch the card or put smudges all over it.