There is also a concern that a D600 will be a step back after the D300. I would certainly miss the ability to zoom in instantly with the centre button and i like the four baks of the D300, and wonder whether two would be enough. Maybe what i am saying is I would love a D800? Or that a D400 would keep me happy??
Would be interested in hearing from those who have made the switch from the D300 to the D600. Do you miss the functionality of the D300?
Re Brian's point I really avoid the 17-55mm a bit as it's so heavy. If I went FX I'd use my primes, and my primes would work well in an FX set-up. Tonight for example I'm shooting at our halloween event using a 50mm f/1.4 and my Fuji X100.
No need for a 300mm either as one can always crop back to what the D300 would have given, and I have a TC too.
Low light ability, dynamic range, subject isolation, viewfinder... all very tempting.. but a decision not to be taken lightly.