I was fortunate to get my hands on a 1dx mark II a few weeks ago, along with an underwater housing for it. Did a last minute trip to the Philippines to test this out.
It is a short video, and I did a mix of macro and wide angle. I used the 100mm F2.8L and some shots with a +10 diopter on it. For Wide angle I used the 16-35mm F4L. Make sure to choose 4k on the playback options.
I severely underestimated what the move to 4k was going to bring. The amount of resources both from a speed and storage standpoint is massive. After 40 dives, I came back with about 3.5TB worth of data. Almost all of these shots were shot 4k and 60p, played back at 30p.
Let me know what you think!