Back to the OP's subject , 5D3 versus the 7D for birding: given the choice, and the evidence so far presented, todays 7D wins. However, my vote is for a 7D2 announced late in 2012 (purely CR -1 I have no idea what I'm talking about). But my thinking here is that (1) its due. 7D is three years old and behind on sensor technology (2) the 7D series could replace the xxd series and become a real upper-end 1.6. and (3) such a body would easily out-perform today's 5D3 in distance-limited situations using the same glass, where a post crop of the 5D3 would just not have enough pixels "on the bird".