DX vs FX

Hi all,

I have to confess I am thoroughly confused with all this... I own a D7000 and am in the market for a second body. Now the D600 comes out and I am left scratching my head. The thing is, I mostly photograph birds (Sigma 150-500, Nikon 80-400, Nikon 70-200 VR II + TC 2x), making any crop factor extremely useful for me. Would there be any real advantage for me to get the D600 as a second body or, given the nature of my photography, would it be more advisable to either get a second D7000 or wait for its successor?
--
Elsie
'The more I want to get something done, the less I call it work.' - R.B.