I have no experience with the Cummins but, I do know that our Duetz powered R-72 takes about 7.75 gallons_hr. I feel that is pretty good considering one can travel 5+ mph (Could go much faster if sickel could keep up) with a 30' flex head in soybeans. At 5 mph that is about 18 acres_hour. Which results in .43 gallons_acre to harvest (unloading time and fuel not included). In short, it takes us between .8-1 gallon_acre to harvest corn. I've heard that the fuel economy of the Cummins isn't even close to that of the Duetz however, the emmissons restrictions seemed to be have limited the fuel efficency of the Cummins. When the Duetz's where used the restrictions were not as "strict".