We had a 7720 T2 at 1500 hrs and a 1680 with the 466 IH and 900 hrs. 1680 cab is quieter and no feeder dust. 7720 was always bigger after sundown. 7720 was way more reliable, but harder to work on, which was rare. I could write a book on the 1680 repairs nightmare. Many weak components. Due to the straw spreaders, the1680 engine compartment was always full of chaff, airfilter plugged often. The 7720 engine is always clean air filter lasted all season. The 1680 was great in barley, 30% bigger no damage, but similar in wheat loss due to unthreshed loss. We used cover plates, new bars, tight concave but no solution found. In canola the 1680 always had shoe loss, so was smaller than the 7720. Both had airfoils. The rotor drive was never positive despite lots of new parts. Stressful to drive at capacity. Traded on 9500, and never looked back.