With the majority of the combining in corn, the standard rotor is the preferred rotor. The speciality rotor will do more damage to the kernal than the standard rotor in corn.
We have had 1640, 1660, and 2 - 2366's all with specialtiy rotor. 1660 had gorden bars which did not wear very fast. We do wheat, corn, soybeans,barley, canolla and white beans with our machine.