A Japanese blog called mono-logueposted some videos comparing 5D mark II and III on high ISO settings. The results are amazing and show enormous improvement on the latest camera.
For better observation of the quality be sure to watch in Full HD and Full Screen. For users reading from mobile devices the YouTube video might be a better option. Also consider that both Vimeo and YouTube compress the video quite a lot, so there is some softness that should not be seen on original footage.
EOS 5D Mark IIIとEOS 5D Mark IIの高感度比較（動画時）
撮影に使用したEOS 5D Mark IIIはβ機です。
YouTubeアップに伴い、再圧縮していますので本来の画質とは異なります。
http://mono-logue.air-nifty.com
Youtube Video
The MarkII series was already excellent in high ISO video, but the decent noise threshold is now pushed from 6400 to 25600 in the new version. At the present time the best performers in high ISO video were Canon C300 and Sony FS100, but if we consider a ‘conversion’ to DSLR quality, the 20000 ISO would translate to something closer to 6400. It is true that the gigantic downscaling from 4k video produces a cleaner 1080 video, as it is also true when evaluating DSLRs.
The best part is to imagine where this run for the crown of best low light video performance will take the manufacturers. The greatest winners will obviously be the users, with sharper results from more and more amazing cameras.
