Hey, Matt. Based on the explanation in your second post, it seems like the 100-400 would be ideal for you. If I shot Canon that would surely be in my locker. For larger wildlife I shoot the Nikon 200-400 on a full frame body and also carry a 70-200 with a 1.5 crop body attached. With 100-400 I could eliminate the second body/lens combo.
Now you DO realize, don't you, that when you get the new lens you are immediately going to want a second body so you can cover the whole gamut without changing lenses. And so it goes...