>It's really hard to decide between the D7100 and the D600. >Lens cost is my biggest concern. I have all the lenses I need >for DX, but no wide angle FX lenses. I think the smart thing >to do is to stay with DX.
I like the 1.5x effect on the long end, and I have great DX super-wide and wide-angle zooms (Sigma 8-16mm; Tamron 17-50mm).
The results on my D7000 are just what I'm looking for, and to achieve the same things with FX lenses would cost quite a bit.
There is the law of diminishing returns, plus I'd lose the 1.5x factor added to my Nikon 300mm.