Its definatly an impressive shot, however its also a shot that has been set up to make the camera/lens look as good as possible keep in mind.
The way the shot is composed and the apeture used results in the corners of the frame, which are also the corners of the net not really being in the plane of focus nor having any real detail.
Shooting real subjects almost always makes the corners look better than brick walls right LOL
Again, while its a nice very nice image, and yes very clean for ISO6400 as well, its again important to keep in mind that it was strobed so its a nice clean light and also the exposure was carefully dialed in to keep from getting too many blocked up shadows.
Point is, shooting that shot at ISO6400 and shooting an ISO6400 shot natural light at a football night game with lots of shadows are going to give very different images in terms of noise levels.
I don't have a D3 but I did some test with my Canon 5D at ISO3200 and -1 EC for effective 6400 and if you light a scene really well, with a few strobes and expose for the highlights, its amazingly clean. Take the same shot under more typical conditions and it starts to get a little ugly.
To sum it all up, the D3 will be an awesome camera no doubt, however don't go expecting to go to a pee wee ice rink and simply shoot ambient light at ISO6400 and have it look that good. It won't. It will be far noiser, you'll have color cast to deal with as well.
Still it will be worlds better than anything you've shot before so these are indeed exciting times
