I made an account just to help out xeveserpere as a fellow human being using these forums for the right reasons (asking for opinions based on experience or technical knowledge in order to weigh purchase options).
Waddizzle if you haven't used either camera for video and can't speak to the question (which is a valid one), I think your work is done here. Thanks for making the world a better place for uh, yourself.
My view from the footage I've seen is that the IQ between the two cameras is basically the same, as was the case with the 6D and the 5D mk iii, which I intercut all the time.
There are some very talented people who swear by the 1DX mark ii for video, most famously Parker Wahlbeck: https://www.youtube.com/watch?v=sS4AtIDJtoE
That said, he got it before the 5d mark iv came out. To my eye, the 1080p footage looks the same, they have equal autofocus capabilities, and they both have high frame rates. Neither will be as crisp as a C-series cine camera, but they will be full frame... in 1080p.
Here, in my view, are the video differences:
-C-Log: the 5D mark iv can be upgraded to include C-Log as an option, which isn't in the cards at this point for the 1DX mark ii.
-4K crop: the 1dx mk ii has a 4k crop factor of 1.3x, whereas the 5D mark iv has a 4k crop factor of 1.74x or something
-120fps: the 1dx mk ii can do this at 1080p, while the 5d mark ii can only do this at 720p
As I currently shoot 1080p for clients that are ok with DSLR-level image quality, the 5D mark iv looks great to me. But I might wait for the C200 to see if that will fit my needs.
The 1DC might make sense for you too, but it has its own drawbacks, such as price of course.
12/05/2023: New firmware updates are available.
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.