We rented a 1dx short term to test, then for three weeks on two separate projects.
I worked so well for us for on figure fashion, lifestyle, cinemagraphs and cut frame video that we bought it and are selling our 1ds3's as comparing the files side by side there is very little difference in real world detail.
The 1dx is equal or better than Nikon autofocus and it just doesn't hit a buffer in real work shooting.
It also seems to have less "smoothness" either from a less pronounced aa filter or maybe the processing, don't know, just know it's sharper.
It produces a beautiful color look and I love the tones.
It doesn't replace medium format for working a file deep, but it is a robust file.
The High iso is insane. You loose some color and the noise reduction smooths the file out some, but you really can shoot in available darkness.
I thought about buying another Nikon and have a full set of nikon lenses, but find Nikon color for skin tones to be way to candy colored and bias towards the reds/orange unless you use NIK software and I'd rather have a root canal than mess with NIK software.
It also tethers with ethernet with is really fast and robust.
The video is good, better than our 5d2 though the only drawback on video is there is no real time headphone play unless you go to a separate recorder.
Speaking of video there is a market for cinemagraphs, which is easier with a still camera or as easy than a 4k motion camera.
(we didn't shoot this and I don't know what camera was used)
Our we use 15fps still images to do cut frame video
(we did shoot this)http://spotsinthebox.com/magic/
Basically what I'm saying is the camera covers a lot of territory and though I used Nikon in the film days, have owned 4 Nikon digital cameras.
In digital I've never warmed up to Nikons like Canons.
One reason is the toggle to flip through images always confounds me and secondly the lcd blanks out when tethering.