Award-winning photojournalist and videographer Dan Chung from DSLR News Shooter has just posted a video shootout pitting the Canon EOS 5D Mark III against the Nikon D800. In the interesting and in-depth article accompanying it, Chung looks at the video features of both cameras in detail and compares them, not only in terms of output quality, but also usability.
News: Digital Photography Review (dpreview.com)