Thanks for the comments.
Sensor technology wise the D7200 slaughters the D700 having a lower read noise at ISO100 (~2.1e-) than ISO1600 (~4.2e-) so the dynamic range of the D7200 is a little higher at ~13.85 vs ~10.
To give a bit of an idea of the optical cover up the D700 has, here is a comparison taken with my Nikkor 85mm F/1.8G lens, same subject but different cameras.
D700 @ F/1.8
D7200 @ F/4
Personally I think the best range for FX sensors is between 24-36mp (D750-D810), larger than that and it really starts stressing many of the lens' on the market.
Might do a little testing tonight and see how it gets. 1s exposures at ISO1600 should be all that's needed at F/1.4
