So most of you consider D700 over D600?but I heard D700 is discontinued already right? How much D700 new body?
I am not sure the money is worth for old tech + 2nd hand?(D700) or new tech yet still have flaws (D600)

What are the advantages of FX? If I can own FX body but not the lens, can use DX lens temporary?

I am using D90, if upgrade one shot go for FX which recommended by my friend. Saving money ><....

D600 is designed in such a way that it becomes as light as possible as a FX camera right?
The built quality I think will surely not be comparable to D700, D800 or above~
That said, I think the built of the D600 is very impressive already, living up to its name as a Nikon