I'd beware of anyone out to prove a point with deliberately doctored images in a internet forum. The 5D Mark II image is either doctored or from a damaged or defective camera. A 5D mark II does not have poor images like those shown.
However, I will say that Low ISO, the D800 does have a lot of usable DR, but at High ISO, it has less than the 5D MK III. It tends to be more important at very high ISO's for me than at low ISO's, but thats just me.
Here is a image from my D800 which really suprised me with its ability to capture a interior along with a bright sunny outdoors.
Do not get rude, I have 2 x 5dmk2 and they show this pattern noise, I have tested cameras since 1978, scanners since 1990 and digital cameras since they come so I know what Im doing.
5dmk2 mk3 has 11 stops DR and then the pattern noise are not including in the measure. Nikon has 14stopshttp://www.sensorgen.info/CanonEOS_5D_MkIII.htmlhttp://www.sensorgen.info/CanonEOS_5D_MkII.htmlhttp://www.sensorgen.info/NikonD7000.htmlhttp://www.sensorgen.info/NikonD800.html
Rude? Are those your images? Posting obviously altered images seems to me to be rude.
I have been into photography for quite a few more years than you, started on digital earlier, and have owned or used many digital cameras, including two 5D Mark II's, two 5D Mark III's and a D800.
I've never seen the banding like that shown in the images, except on forums where the images were under exposed and then pulled up several stops. You have to really manipulate the images in post, or have a defective camera. If your 5D Mark II's produce images like those with a proper exposure, and you did not send them back
I'd prefer to see information from and intrepreterted by the actual tester.
Sensorgen.org charts are derived DXO information, just a repeat of the same info.
"One source, the one which is used for the data on this site is DxOmark.com
DXO's own chart illustrates the higher DR for the 5D Mark III at high ISO's and the excellent DR for the D800 at low ISO's. It pretty well matches what I've seen with my cameras.