I have both 1Dx and 5d III (and had 7d till I upgraded to 7d II yesterday
Had the afternoon off so spent an hour with manual, adjusting custom controls, etc.,
Shot a high school volleyball match last PM after using to photo a few deer at twilight from my deer blind.
The pro's / con's between 5d III and 7d II will be debated / rehashed here for awhile I am sure.
From the pure practical aspect of shooting, I enjoyed the familiar Canon build, ergonomics, customizability, and wrt to the 7d II vs the 5d III, the increase in FPS was appreciated. The AF functioning (capture rate) was really no better, though the few extra AF points did make positioning the points more convenient/easier.
What I did notice from shooting within my darkened deer blind, and shooting out to an apple orchard with the 200-400, was that there was some 'focus hunting' with both bodies UNTIL I placed camera / lens out the peephole completely. The AF IR sensor was very insensitive without a direct line of sight. May seem obvious,maybe it is only with a long super telephoto, but it bummed me out that my lens had to be almost sticking out to grab focus.
Anyways, on topic for the OP, the FPS / extra reach are definite value - adds, but offset by need for higher ISO, and (subjectively) a sl drop in resolution/crispness and I'm still not sure about color rendering after only 1 shoot . I usually set custom WB, but did not yesterday
I am hoping once I AFMA my gear, and ACR is available for the RAW files, the crispness will improve, and I can set custom color profile from within LR. Too busy to set one up directly via DNG from within Color passport last PM.
I am shooting an all day tournament tomorrow so will post head - head comparisons of all 4 of my bodies next week. The hassle of DPP batch processing will delay my posting the 7d files a little as I am on a paper deadline, so will be concentrating on the 1dx files first, but as time allows I will add them to my canonrumors website (www.navb.phanfare.com/canonrumors
) for your viewing pleasure