Pixel density on the D700 is significantly lower so you could expect to see the D800 delivering more detail with top lenses (among which the 24 - 70 is one).
Good comment re being a pixel peeper. To the maximum size of presentation most people want to prepare (or are even able to) I doubt very much there is significant visible difference between a D700 and D800 image. Up to an 11 X 17 print or even a bit larger the D700 should have no problem providing everything an inkjet can render, to say nothing of even a high definition monitor which typically has only about 100 pixels/inch (at 100% you would have to massively scroll the image to see all of it).
Where the D800 really shines is when you start printing at 24 - 30 inches on a side or if you need to crop. That's when it pulls away from the crowd and invades medium format territory.
The D800 has made a digital believer out of me, coming from medium format film. It has proved worth every penny, making possible what I had thought digital could not deliver for a long time yet. It's an extremely enjoyable and in some was liberating product, making photography that much more fun. Beware the principle down-side (according to some)which is a rather low burst rate although I find it plenty fast enough.
The D800 also raises the bar on dynamic range. Last summer I shot an entire wedding at ISO 4000 (no flash allowed, even for the pro) and every image was stunning - sharp and noise free to the extent no one except a pixel-peeper would spot it.