Upload & Sell: Off
I'm surprised you say that, I thought 5DIII could be used for everything as well as the 7D does, equal at birds and better at everything else. My other choice is to go with my 1DIII
Yes, the 5D3 can be used for everything, but there are bodies better than it at some things.
The 5D3's strong points for me are its 6 fps, great AF (down to f/8), excellent IQ and small size (compared to 1D series).
The other advantage of the 5D3 not often mentioned is compositional flexibility in post processing. I can place the bird in the central portion of the frame and have the option to present the image in landscape or portrait (with still enough res left to print large), depending on the requirement of the end-user. These advantages make the 5D3 a good complement to my 7D and 1D4, at the subjects I shoot (mainly birds, surfing and macros).
That said, if I were forced to use only one body at birding and landscape, I'd opt for the 7D because of pixel density, 8 fps, many AF points, small size and the UI. Reach is king at birding. At landscapes (whose elements often don't take to the air) I can use a tripod and shoot at low ISOs. I can likewise stitch if my Aps-C FOV isn't wide enough.