I have no idea whether this is the right forum, but wanted to share my thought process with others. I'm on the wait list for the D600 at Berger Brothers - the same place I got my D800E.
I shoot a lot of IR with a converted D200. Rather than converting an existing D300 or D7000, I am going to convert a new D600. The thought process is that most of my IR work is landscapes and architecture - and these subjects are great with the larger FX sensor and large number of pixels. The rumored features of the D600 appear to line up pretty well - it's new technology and probably cheaper than a used D700. And it will share a common battery and accessories with my D800E and D7000.
There are certainly some reasons to go with a D700, but the larger file size of the new cameras is a real plus for landscapes and IR. And the D700/D3 has a light leak issue for IR at higher ISO levels (above ISO 1600).