.Now with a 5D3 I feel like a magician.
I agree with this completely! I too came from the 7D and, when paired with the 24-70 II, I feel like I'm cheating when I shoot with the 5DIII. This combo removes any barriers (read excuses) for bad photography. If you can't take good photos with this, you can't take good photos with anything.
As for the OP's question, I used the 16-35 on my 7D and did quite well with it. However, the range is very limited...you need to get right in people's faces and that can distort them...not in a good way. You also won't get the kind of blurred background you might want want to separate your subject.
My typical setup now is a 24-70 on the 5DIII and a 70-200 on the 7D. That gives me a 40mm "hole" between 70 and (effectively) 110 but it hasn't been a problem.