I can now state with authority that the 6D is *not* a good body for BIF shots. That buffer is lame. I was shooting some bald eagles today (pics in a bit, hopefully) and I was missing shots because the buffer took so long to clear. I was even being judicious with the number of shots. I switched over to the 7D and was again amazed at how it can pump out 8FPS and just keep going. I throttled back to 4FPS and never once hit the buffer limit. That expanded AF point is nice, too.
On the downside, I was reviewing some of the last shots I took when the 7D screen went black. No power, no lights, no nothing. I'm hoping it's just dead batteries, but it had two in it and when I first fired it up the battery meter looked to be on full. I didn't bother to swap them out with the 6D's because I was heading home anyway. Fingers crossed.
EDIT: Whew, just dead batteries.