http://ohe.cat.com/cda/files/1271302/7/LEHT8895-00.pdf. This is the horsepower - torque curve charts.
Flat torque curve means longer you can hold a ground speed MPH with out losing engine rpm. I think it will be interesting to see the relationship between the higher horsepower- flatter torque curve and fuel mileage. I still think mileage should drop as available horsepower goes up, but maybe the flatter torque curve helps negate that.