Unless anyone has a raw-image to process, this thread has no poin to it...
From what I saw yesterday, the difference in chroma noise is very substantial. I made sure to turn off all NR in camera. Shooting at 12800 looks so much better than the mk4 it's crazy... And I gotta say, just comparing DxO marks is stupid. I've seen lots of examples where they rate something and it's not what you see in real life. More color-noise is better than more luminance noise, easier to remove. Besides, the LOOK of the noise is also VERY important for the final image.
From what I saw trying the 1d X yesterday, it is a huge improvement.
Another thing, high iso's are not just for shooting in the dark. It's to decrease shutterspeed in normal light, and I tried at iso 12800 in a well lit store to get very fast shutter, and it was nearly no noise at all.