For the guy who produced the video in which he concludes he is better off with the 100 - 400 ii on the 7d 2 than using his 5D mark 4, I suggest you add a Sigma 150 - 600 onto your 5D 4 and use this equipment combo to compare against the 7D ii arrangement above, then get back to me. The Sigma/Canon combo will be 40 mm short, but still pretty close to bang on for a good comparison. Then when you are done all that, add the 1.4 TC to the Sigma 150 - 600 and let me know how it goes compared to the 7D 2 and 100 - 400 ii.