but the AF of the 5d3 is way better than that on the mk4. IQ is much better, and also the goodness of fullframe. And a lot of the things of the 1-series is included in the 5d; MUCH less shutter lag, MUCH less blackout time, dual card slots, zoom in directly to 100% at the focuspoint used.customization of buttons, big bright 100% VF, better battery, I get 1000 shots. Setting auto-iso range and use it in m-mode. New advanced codecs for video, audio-feedback, audio-level control. A dedicated switch between Servo and One shot, spot-af with all lenses. Setting the lower shutter speed limit (although not fully customizeable). Proper placement and size of the dof-button. And I'm sure others will think of a few other things.
Please define 'way better AF' than the current AF king?
Shutter lag - you must be joking
"Setting the lower shutter speed limit (although not fully customizeable)" - it is on the 1D4 which combined with the other settings gives the equivalent of M with EC
1000 shots per battery - I would be horrified if the 1D4 didn't get 2000
In fact in nearly everything the 5DIII struggles to match the 1D4
I notice you have left out the areas where the 1D4 walks over the 5DIII, ie fps, f/8 focussing, af point metering, 8 point af selection metering
The only point that the 5DIII scores is the point AF for all lens - is that a major dealmaker? Not for many I think