DPReview has added a page of tests and discussion of the 5Ds with regard to dynamic range:
http://www.dpreview.com/previews/canon-eos-5ds-sr/7
In summary, a slight improvement but not up to the level of cameras equipped with Sony sensors. They attribute the difference to off chip A/D converters on the Canon cameras vs integrated on chip A/D coverters on Sony sensored cameras.
Thanks for the link. Those dpreview comparisons really highlight the deficiencies of the 5DSR dynamic range compared with Nikon cameras.
The impression I get is, if you're shooting a contrasty scene with a DR (or Subject Brightness Range) of 6 stops or greater, and you want to raise the deepest shadows, then the 5DSR will show significantly more noise in those shadows than the cropped-format Nikon D7200.
As I understand, the 5DSR pixel is of similar quality to the 7d Mk II pixel. There might be a slight improvement, maybe 0.1 or 0.2 EV better, but let's get things into perspective. Any improvement less than 0.5 EV is not worth getting excited about.
The Nikon D7200 pixel is slightly smaller than the Canon 7D2 pixel, yet it's DR is 2.68 EV better at ISO 100. At ISO 800, the DR of the D7200 pixel is still around 1 EV better than the 7D2 pixel.
The images below tell the story.