Well, there are alot of people on here with knowledge with those machines, but to get an educated answer you will need tell us how many acres of what crops you are going to be harvesting and expected yields. Also is you land hilly or flat? What are you going to be trading for this combine and are you expecting the same capacity, or more or less capacity? Few more details and i'll bet you get some great feedback.
i would go with the 7120 i know its more money but if your going to keep it for a few years i would buy 7120.self leveling seives,direct drive rotor, no belts to me i think it would be worth the extra money. i think you would be happy you went that way.also i think resale will be higher on 7120 when you go to upgrade. with that said i like both models just would lean towards 7120. good luck on what ever one you buy what are you running now.