Many people seem to think its the 6MT that contributes to the slightly lower mileage with the MR, but I was looking at the gear ratios for the 5MT and the 6MT, and 1st thru 4th have virtually the exact same ratios on the 5MT and 6MT. And since 6th gear on the MR has a higher gear ratio than 5th on the RS/GSR, which should be better for highway mileage. I'm wondering if the slightly lower mileage is due to something else such the additional aero stuff on the car. It takes energy to create downforce, and the energy doesn't come from nowhere.