d800 needs to be excellent at iso 6400

really want to get into night photography/astrophotography, from research I have done you need very clean iso 6400 to get a fast enough shutter speed to get a fast enough shutter speed so you can capture the stars prior to movement appearing on the stars. I think it is around 5 seconds. I see excellent examples with 3ds at iso 6400.

I really hope d800 is as good as 3ds at iso 6400. It would seem from some examples shown that with the extra resolution and the very clean high iso samples shown so far that I am going to be in luck. Of course the d4 will be excellent, but was hoping to not spend that much.