New lens for d3100 fx compatable...
High iso I have heard is about 1-2 stops better than the d7000. I often find myself shooting at 6400 iso and would like quite clean images at that. Bigger brighter viewfinder, although I know the d7000 has a bigger one than the d3100 it's still not all that big. Quality of the lenses also has a major factor in my decision as the dx line up is a bit shabby to say the least. Also gives me options with the dx mode and fx mode.