All that said the D800 is a heavy camera - you will see yourself how convenient it is to use with NN3. NN4 is more appropriate for this camera.
Note that most likely (I haven't tested it) there won't be enough space to rotate the camera fully up - the camera will snag on the NN3 lower rail or the rotator knob.
Photos came really good - lots of detail. But have checked stiching in ptgui and its not bril! had a look at the settings and think (jvr) that the calculations are a bit off. here's what I've come up with:
Settings for D70s with NN3 mk2 and cp1 with sigma 3.5mm lens:
Difference between D70 and D800 (from entrance pupil database):
Therefore I calculate that the correct settings for D800 nn3 mk2 with cp1 and sigma 3.5 are:
Hope this is correct!
jvr - you are right it is a close fit when moving the camera for Zenith and Nadir shots may have to invest in a bigger mount!
As a matter of interest what's your preferred shooting setup? I'm playing around with either up or down 10-15 degrees for the horizontal shots - trying to decide what is easiest to edit in photoshop etc..