Except if you are into bird photography, air show photography or surfing photography, I don't really see the point of any lenses above 300mm.
They are expensive, they are heavy and cumbersome, they permanently require a steady support, and you attract a lot of attention (some like it though).
I think the core focal ranges of 35mm photography remains between 14mm to 200mm, where the choice of lenses should be more driven by perspective and compression effects rather than 'getting closer to the subject' or 'fitting everything in the frame'.
With the D800, the possibilities of large printing and heavy cropping are quite interesting. And perhaps thanks to the D800, you won't be contemplating that $70,000 lens anymore which would have collected dust in your shelve anyway.