Upload & Sell: Off
Personally, I have to have my second body be the same model as my first, especially if I take both into the field. But I'm a bit of an old fogey anyway.
I prefer having "different horses for different courses"... full frame, 1.3x sensor, and 1.6x sensor (5D3, 1D Mk4, 7D).
Sometimes it's nice to get extra reach or different feature that you primary body doesn't have. If the OP shoots wildlife, then the 1.6x reach of the 7D (without the loss of a stop from a TC) might be nice to have, especially since the 7D uses the same battery and charger as the 5D2/5D3.