I took the F6 out with a roll of Ektar 100 and my 24-70 zoom yesterday. What struck me most after using my D700 is how quiet it is. The D700's mirror snaps sharply while the F6's just pops, and the motordrive is hardly noticible.
It might be kinda like the difference between an F4 and a D1H (or F5). To me, the F4 sounds like a quiet sneeze when fired, whereas the F5 (or a D1H, or F100) will be a bit louder, almost like an F3. In fact, the F5's I've owned, when fired in Cs mode reminded me of a Nikon F3 with MD-4. That said, they're still quieter than the FM2n, FE2, or FA.
The D700's mirror snap makes the whole process much louder than the F6 to my ears. I don't know how they differ at distance however.
The F4 is quiet but the winder rings in my camera. The F5 makes a clop. The loudest to my ears is either the FM2 MD-12 or the F2 with MD-2. Those are just obnoxiously loud. The F3 isn't much better for sure.