One of the users on Nikon Cafe had access to a D4 and D800 and has posted some sample images with a range of ISO tests on their website
http://www.nikonuser.info/fotoforum/viewtopic.php?f=33&t=1507&sid=6443c4d27d7e22cafce29a63a0d0a101
http://www.nikonuser.info/fotoforum/viewtopic.php?f=33&t=1507&sid=6443c4d27d7e22cafce29a63a0d0a101