The speeds listed are much slower than most bin unloads are running.         If you look at the asterisks for the RPM  it says   



**Augers with intermediate discharges should run at the speeds shown. Higher RPM may cause the conveyed material to be carried across intermediate discharges. 



So you probably could run them faster if you're not using an intermediate drop, or grain being carried past isn't going to cause a problem.       A phone call to Sudenga would probably get the best answer to your questions.