Very interesting question Rob, depending on line (and column?) skipping or binning and all that complicated "stuff" required to downsize the FX resolution down to the approx 2mp video frame size.
It seems like only testing may provide some clues, since manufacturers seem to consider the "stuff" a highly proprietary matter.
I am also more than interested to see how well the video noise reduction works - since Nikon is taking some effort to point out this feature, it sounds promising.
One final comment - that 2.7 crop video that the D4 does, that may be the best quality video in that no smushing occurs to form the video frame . Then pump the output uncompressed through HDMI and it may be a seriously beneficial feature.