For best results on d800 low light shooting: Push in post or shoot high iso?

It's come to my understanding that shooting at above iso 400 may be pointless for the d800.

This is because -- to my understanding -- the image will retain all the information needed to meet or surpass the same shot taken at a very high iso. (say, 6400)  I'm suggesting that the lower iso image will be able to be pushed many stops in post via post processing software like lightroom 4 or etc...

With that said, a couple questions:

A) Is there any truth to my assumption?

B) If so... at what iso should we draw the line... where does post processing + low iso become the source of the better image?

C) Has anybody done any night sky shooting (stars and whatnot) with this application in mind? Say... taking a shot at 200-400 iso and pushing stops all the way to, say,  iso 3200 or 6400 levels? What were the results like?

I'm basically trying to figure out if I can achieve *BETTER*low light performance from the d800 on night sky shots by shooting low iso and pushing heavily in post. Or will pushing in post just give me (at some threshold) the same result I would've achieve at X iso.  (and thus... no real improvement, only more flexibility in determining "iso" in post)

Hopefully this makes some sense. Not a sensor guru here, just did a bit of reading and was wondering what performance could be theoretically as well as practically. (hoping somebody has tried such experiments)

I'm trying to figure out how to get the most out of the d800 for night-time landscape shooting. (don't own one, yet)