DPReview has posted their first studio tests with the Canon EOS-1D X Mark II. They have tested RAW dynamic range performance as well as ISO to give you an idea just how good the new 20.2mp Canon sensor is.
The Canon EOS-1D X Mark II shows very similar amounts of noise to the excellent sensor in the Sony a7R II up until a 3EV push, with the Canon dropping behind after a 4EV push. It's a similar story against the likes of the Nikon D750 or D810. This means that the darker shadows in a processed image would be slightly cleaner in images from these cameras, after contrast adjustments or a less extreme push.
However, this performance is noticeably better than the Canon EOS 5DS R and, significantly, better than the 1D X II's most direct rival: the Nikon D5. See the full studio test
Although the 1D-X II shows significant increase in dynamic range at low ISOs in our dynamic range tests, high ISO Raw performance remains fairly similar to its predecessor, falling behind the Nikon D5, and even slightly behind the 42MP Sony a7R II, at very high ISOs. See the full studio test
There will likely be a lot of comparison tests and reviews rolling out in the coming weeks. I haven't received my EOS-1D X Mark II yet, so I'll just enjoy reading about it for now. :)