I moved from the 7D to the 5D MkIII (with a couple of mirrorless cameras in between) and find the 5DIII to be an absolutely wonderful, most capable camera. I looked briefly at the 6D but preferred the 61pt AF to the 11pt, as I didn't want to have to rely mainly on the center AF point. I know that the 6D is considered to be a better performer at high ISOs, but the 5DIII is quite impressive itself! I don't have any plan to get the 5DIV anytime soon, unless I find that there is a need that my 5DIII can't meet, but so far that need has not become apparent. It's a fantastic camera!
Andy
Andy