They are mixed because a 30 foot is not ideal. But, yes, it will handle it. Is your unloading augar long enough?
The ideal speed is the one that allows good feeding without unacceptable loss or quality.
The way to address that with the 30 foot is to take less cut (back to 25-27 or less) when beans are too heavy or too short to keep speed up, or whatever conditions you are dealing with.
50-60 bushel beans can cover a variety of plant size. If you are cutting waist or chest high plants, you will have to go slower or take less cut. If they are short, you may able to cut right along. Green stem, slow way down.
The answer will be obivious when you are in the field.