The wacky dudes at crisislab.com did a rather strange (and with questionable taste to my liking) video comparing Canon 5D3 and Nikon D800. Although I really don’t like some things on the direction side of the video, the comparison is pretty well done and makes the video worth it.
One important advisory: consider the video test with some caution, as they’ve put some gimmicks to simulate some high ISO. Despite this, Canon 5D3 is well known for outperforming Nikon on high ISO DSLR video.
Just as a reminder, I do not endorse or advertise any brand. That said, I agree 100% with crisislab’s conclusions.