I've rented the Lens Rentals "Lightweight Tripod Kit", which is a Q3 on a set of Velbon El Carmagne 640 legs. I used it with a 1D Mark III and 70-200, so similar weight but not the challenge of a shifting center of gravity. I'd guess that a Q3 is fine for you, but would just suggest getting an appropriately long lens plate for the 100-400.


Although pricey, I plan to get a Really Right Stuff L-plate for each of my cameras. I don't like the weight of the camera and lens off-center when the ballhead is rotated for portrait orientation, so the L-plate would fix that.