case has a chart on their advantage case site http://www.advantagecaseih.com/?utm_sour....aign=CaseIH_com . If you have hilly land i would probably go with a 7120 or an 8120. Since you are gonna run a 40 foot header you would be able to justifiy the 8120's horsepower especially if you are chopping the straw in a good crop.