I sold my excellent mint copy last week while I can still get a good price. Whereas it is OK on FF, DxO gives it a rating of 13 Mpix sharpness on the 6D or 5DIII, it drops to only 6 Mpix on the 7D or 7Mpix on the 70D, echoing what most of us know already that crop requires sharp lenses. And, I found the 100-400 on the 5DIII pretty good and not so good on the 7D,http://www.dxomark.com/Lenses/Canon/Canon-EF-100-400mm-F45-56L-IS-USM-mounted-on-Canon-EOS-7D__619
A supersharp lens like the 330/2.8 II drops from 21 Mpix on the 5DIII to a still excellent 14 on the 7D and 17 on the 70D. Ok, DxO tests aren't perfect and they can make mistakes, but testing the same lens on different bodies is a pretty fair comparison.
If I want zoom in the 100-400mm region, I am going to use as a stop gap until a new 100-400 or what else the 70-200mm f/4 IS with or without extenders. I found it better or at least as good as the 100-400 on the 5DIII, and you can see this is general on the TDP site or lenstip, and not just me.
5D IV, 5DS R, 7D II, EOS-M, Powershot G3 X, 400mm DO II, 300/2.8 II, 1.4xTC III, 2xTC III, EF 1.8 STM, EF 70-200/4 IS, EF 24-105, 15-85, 100-400 II, Sigma 10-20, Sigma 150-600mm C, EOS-M5 15-45, f/2 22, 11-22, Samyang 8mm f/2.8 fisheye