In a thread here http://www.canonrumors.com/forum/index.php?topic=24210.15As has already been pointed out you are comparing two different formats. If on the other hand you compare the 7DII + 100-400II with the 60D + 70-200 2.8II ( a lens that is often referred to as Canon's best zoom and one of the best made by anyone) at 100mm the 7DII combo is easily better wide open and even with the 70-200 stopped down to f4 the 7D 100-400 is still marginally better in corners and mid frame, 70-200 winning the center. Being compared to a best ever lens on the same sensor format with that kind of result, how good does it have to be to impress?
and in the test-chart sample images available at the-digital-picture, certain lenses seem less sharp, soft in comparison, when mounted on a 7DII and compared with a 1D Mk III. In particular, the new 100-400mm II
I wasn't criticizing the lens. Surprised at the difference in quality between formats. I'm buying a 7DII primarly for reach with long lenses (although I'm sure the fast fps will come in handy) in order to use TC's less, or use 1.4 TC more and 2.0 TC less. If the 7D II adds that much CA, I might as well save the money and just use the TC's.
I'm not going to argue that the 7DII is a better camera than the 5DIII, while it may have a couple extra features useful to some, it is not "better" overall. I can only justify one body, so if I had the 5DIII like you, I'd be looking at the 1.4X option too. If you are happy with two bodies for unique uses, then look again at the TDP comparison and set the FF image to 560mm and the 7DII to f8. They are quite comparable and the 7D has all 65 AF points to use and a stop to open up if you need more shutter. The center point is still available beyond that, with the 1.4X. Isn't CA one of the easiest lens faults to eliminate in post?
I'll admit to bias, I bought a 7DII in December and I'm happy with it. I don't shoot small things, maybe that is the difference, it did work very well with a 135L at an NFL game as a fan. I did not experience the "if the first misses they all miss" as commented here. I had a couple instances of spontaneous moments when the first shot was not focused, the second improved, the rest of the burst in focus.
Sticking to the categories defined in this post, I am a 7D upgrader, so I can't compare the experiences of FF shooting. My plan had been to go to 5DIII when the IV was released, but the f8 AF included on the 7D was the deciding factor. I can't justify the big whites, and 400mm just didn't make the objects big enough for AF to work very well on the 7D (distance not size related). I'm looking forward to picking up a 100-400 II before summer paddling season and seeing what it can do with the 1.4x. I already have the 2x, so I'll keep that too and try it for fun with the live view on stationary/slow things.