You will want max speed so that you get the max sickle strokes so that you can drive as fast as possible. As a rule, it is best to run the feeder as slow as you can get away with, but since you want to drive fast, I assume, you will want the feeder fast. Slow feeder speed reduces wear on a lot of things, thrashes the crop up less before it hits the rotors, improves feeding by passing slugs more slowly, and probably some other things I don't know about. How did you come to have an 86 and a 98 if you don't mind me askingIJ