#2. "RE: Pros and Cons - FX versus DX. Why switch?" In response to In response to 0
The FX format has no magic associated with it...
What I mean by that is that any differences in image quality that we see are not because a camera is FX per se but because of the generation of sensor and processor and the pixel count.
The D700 outperforms the D300 in high-ISO performance because it has much larger photosites (which collect more light) - in other ways they are very similar (I used both alongside each other for some time).
On the other hand, the D800 bests both of them because it uses today's technology, even though it has even smaller photosites than the D300
Unless you have the funds to also swap your 17-55mm DX for something like the 24-70mm Nikkor, you may not see too much benefit from a D700 - especially if you don't often shoot in low light.