I took some time to shoot a comparison between the 1Dx and the 5D Mark II, I found a scene with similar tones, then did a 1600 iso shot with the same settings (default jpg)
It appears the 1Dx and the 5D II have nearly the exact same noise levels, which would make sense considering quantum efficiency is likley very similar.
Here's a back to back comparison of a 100% crop of the 1Dx and a 21mp 5DII shot resized to 18mp. The noise has been enhanced with a high pass filter for easier inspection with an identical setting on the final composite:
useless.. post the originals or nothing.
You know what, I'm not going to this forum is incredibly rude and has no respect for people putting forth the effort to do research.