Planting on a 17" row will give you great production of your corn and beans, and better weed control, but may hamper your fall plantings due to a limited growing season. Planting on a 30" row will reduce your corn and bean yeild, and open up the chance of more weeds, but will give you more room and thus time for your fall plantings to grow. It's a trade off and one only you can really answer as to which is best for your situaton. In either case I stick with clovers, brassica and cereal grains. The amount of time these have to grow is limited by the amount of sunlight they get and that is controlled by how thick your corn and beans are. I time my planting to when the beans start to yellow as I know the amount of light on the ground is increasing and will only get better. Good luck.