Dad has 1660 with some of the '66 updates built in or he has put in himself. He runs it about the 3 o'clock. When I was running it couple weeks ago, I could get the power needle to peg out about the 5 o'clock spot if I was putting the unload auger out and running about 4 mph in 180 bu corn at 19%. But he also has a 10 row 22" 800 series corn head on the front so that takes a little extra power to run.