I used to say the H stood for "Hot Rod". Then the Revolutionary D3 came along. The D3 is a Machine gun. The FullFrame Sensor makes image capture easier. There is 3 times the Pixels to crop from. The ISO is 8 times higher. At 6400 it is better than the D2h at 800.
I had a D300 before the D3 came out. After using the D3, I took back the D300 and got a second D3.