The lens issue is a good point -- you're not going to be happy with the D700 + DX lens. FX format means you'll need FX lenses, and it's better not to go cheap for glass.
My feeling is, the sooner you switch to an FX, the better. I can't see much of a future in the DX line... When sensor costs come down the cost advantage of two lines of VERY similar cameras goes away, and the DX goes away. I switched about five years ago... Fortunately, I have three lenses I no longer use. I bet the probability of the future being all FX is over 99.9%. jD