Here's a really good side-by-side comparison between Canon's EOS 5D mk III (with the Magic Lantern mod) RAW output and the Blackmagic Cinema Camera
This is a great test from Cinema 5D but all the normal caveats about judging video quality from YouTube or Vimeo apply. You can see differences but we think it is inconclusive.
What you certainly can tell is that the RAW output from the 5D Mk III with the Magic Lantern mod is remarkably good!
Before you make a judgement as to which camera system to buy, though, you still have to consider which is the better practical solution: the BMCC, which is fully supported and can record RAW and to ProRes, or the Canon, which will probably never be supported in this mode by Canon.
But practical stuff aside: the field is wide open now.
Kudos to Sebastian Wöber and Johnnie Behiri for this great comparison. More RedShark coverage of this story here.