There are not THAT many differences. The main ones being the wing. A bit longer and more squared. More wing area. The rest of the differences in the airframe (in the fuselage area I mean) are minor by comparison.
FLS, surely you're right. I was attempting to simplify it for comparison's sake. The extra wing area has more parasitic drag, if I've got my terms correct. That probably contributes PART of this 10mph difference. However, 10mph isn't much. You could have 10mph variation out of the factory and still be within acceptible specifications for the military to accept it.