See my post and gallery with the daffodil I shot with the D800 and a Nikon 70-200VR. I was 10 feet away and shot in FX. Then cropped out a postage sized image (in a 4x6 image size for example)and you can see what I got. If I ever tried to do that on my D90 it would be way too grainy and loss of detail. But with the D800 resolution it is acceptable. This was just a quick shot by the way for a test.
Dan (Nikon D800,V2,Sony HX400V,Lumix ZS40) "I don't read, I just look at pictures" - Andy Warhol