I love my D700, and i still have my D300 because i loved that too.
In seriousness, going to FX is a game changer the 700 was for me. I borrowed one and instantly loved it. But DX are Great cameras dont fall into the FX snob trap. At the end of the day Matt you have to look at your budget, and remember cameras will change models with the wind, but good lenses hold there value for a long time.
No doubt pixel peepers will tell you you must have 68, trillion megapixels, but it wont make that much odds unless your printing large! I'm not saying don't go there, just dont let it sway you unduly. (the old, "I would'nt touch that camera cos it only XX megapixels" coconut).
The
second hand 700's and 600''s i guess must be a good deal now, see if you can get hold of one to handle, see how it feels.... D700 is (Was) a Pro camera so its built like a brick out house full magnesium body, i think the 7000 series is some magnesium so there pretty robust. I have used my son's 7000 and thats a nice camera too...
Just remember if your thinking new model i.e. 7200 or whatever they are going to call the thing, wait to see the write up's, dont always assume because its the next in the line its gonna be a "7100 with knobs on" sometimes things go wrong and the succeeding model might not be as good as the previous one.
If your thinking D600, remember some early 600's had issues with the shutter mechanism design, this caused it to flick lubricant off the mechanism onto the sensor, (Hence the D610) so if your looking at a D600 make sure you dont get an affected one.
At the end of the day all these camera are superb, and all have the ability of taking fansastic pictures, so its your budget that will be the dictating factor. If you can lay your hands on the camera your looking at, for a feel, that normally makes a difference, but to be honest Nikon for Nikon you should find easy.
I hope you manage to find the camera you want, good luck with your search!