I've worked 1400, 1600 and 2100 Axial Flows and I also think that increasing the rotor speed is best. I also check the rotor-tach and like to run at anything between 30 and 60 lower than empty speed, this is generally fine. I don't like having to stop for settings every hour, and this is the way that I keep running. As material dries down or dampens, the decrease in rotor speed varies, obviously, but the most important thing to remember is to keep it full. And to conclude, the very best way to know when it's full, is to know your machine well.