If i have all of my numbers correct the D700 @ F/1.4 should be about 12x faster than the D7200 @ F/2.8. This includes me assuming a QE of 40% for the D700 and 60% for the D7200 (newer sensor).
On paper, one 8 hour stint with the D700 should be worth near a fortnight of D7200 8 hour runs!
Of course, there are a lot of things that are nice on paper but don't quite travel well into the real world
