Hi, Mykin
Except for a few bodies like the D70 that have an electronic shutter, Nikon DSLR's shutters are limited to a flash sync of - at best - 1/320th. I currently shoot with D800's (as well as Einsteins as my go-to monos), and slight banding begins to creep in at 1/320th. Even at 1/250th - depending on the situation - I will sometimes see a slight vignetting on one side of the frame caused by the leading edge of the shutter curtain. This is also all consistent with the D200's, D300's, and D700's I have owned.
So, I can't think of any shutter or flash sync variable between your D800 and D4s that would account for the difference.
Craíg
http://www.craigwasselphotoart.com