OK, must admit I have not read all of this thread. Quite a bit, but not all.
I was very unhappy with my 5D MK III. Yep. I was the one. I'm sure you knew there was one shooter who sold it a few weeks after it was released I legitimately felt the images from my 5D II were much superior and after I bought a feature poor but image high 6D to replace it. I am now considering a 5D IV.
Couple of questions:
How is the dynamic range? This was my number 1 complaint with the III. 1 DX much superior and even the 6D and 5D II in my opinion.
Is the exposure in evaluative still highly weighted toward the focus point? That was the second deal breaker. Can it be changed in the IV?
And last, will an L-Bracket from 5D III work on a 5 D IV? Seems it should. Anyone tried? Obviously not a deal breaker on this one.