The D3 is an unbelievable FF camera, for its AF and its outstanding ISO control. The D300S on the other hand has the most poor ISO control I have ever had the misfortune to witness - worse than the 400D (Canon) and the AF is so so. I'm not overly impressed with its constant hunting even with a 70-200mm f/2.8 lens whereas the Canon 1D Mk iiN was amazing and my D3 even more so. I've heard great things about the 7D and used it briefly hence Crop = Canon, FF = Nikon. To say that the D300S at ISO 400 is pathetic is an understatement. I'm only keeping it for the reach.