To date, Nikon users haven't enjoyed the benefits of Magic Lantern hacks appreciated by many Canon shooters. However, this is slowly changing as NikonHacker has added firmware hacks for a variety of Nikon DSLRs. Using recent NikonHacker updates, Lars Steenhoff has shared his own 54Mbps sample, albeit without comparisons for the moment. NikonHacker user, LPowell, however, has shared a series bitrate comparison videos with the Nikon D800.
While privacy settings have not made these available to embed, the videos can be viewed through the links below.
For additional information and a great, simple explanation of video bitrates, see LPowell's discussion on the NikonHackers forum.