We run an 8 row 30" and have ran up to 8 mph in dryland corn, when yields are under 120 bu_acre. We unload a lot at 7 mph, by using the corn rows as a guide the grain cart driver gets in the right row and sets his speed then I just keep the combine over the cart. It takes a good grain cart driver just to keep up at these speeds. We have a lot of fields that are 1_2 mile long, so plenty of room to unload.