In essence are you seriously considering going from DX to FX because of the rumored D600?
I'm very excited about the rumored D600, it's specs and reported estimated MSRP. I've thought about getting a D700, then a used D700, so I could increase the resolution and dynamic range, get higher usable iso and iso ceiling. But most importantly have no crop factor limitations. I'm planning on not selling my D300s DSLR, but that could change after the reviews and my own personal impression of the D600 "DX" abilities and limits. I came to realize the benefits of FX in the last year and have been planning in making the move. The last 2 lenses I've purchased are FX Nikkor's, to the tune of US$3,900, primarily in anticipation of buying a FF DSLR. The D800 nearly became my first FF, but the massive MB of raw images at full resolution kept me from getting it.