Nikon Rumors has published images from Taiwain which purport to show that the Nikon D800 has better high ISO performance than the D700. While that is conceivable (the sensor is four years newer), I'm going to wait until more systematic and detailed tests come out comparing the new 36-megapixel camera to its 12-megapixel predecessor. The pictures from the Taiwanese websie are blurry (on the D700 side) and have been posted and then removed. So take from them what you will. Focus issues aside, the D800 pictures do look substantially cleaner, albeit muddied at ultra-high ISO (those ISOs with numbers so high you probably won't need them).
Below you will find pre-order information for the Nikon D800 and D800E: