adjustable ND filter and the D800

I guess it depends which brand you buy.  another shooter i know uses cameron and is happy.  i got pro-master and am very unhappy.  first, even at 1 stop ND the quality is reduced noticeably.  and at the extreme ND setting, an X appears.  so for in between 1 and 6 or 7 stops, it might be ok.  i suggest you go to the store with your camera, ask them to put it on your lens for you and go outside to take a couple of shots.  then take the ND filter off and repeat those shots.  compare at home. maybe you'll be the happy one.