From stock 15-41 i went to a 14-40 ..not sure im gaining anything but a faster take off . not sure up top .
You'll lose a little top end. I went +2 on the rear of my M750 and it made a nice difference in parking lots and a bit more acceleration. It also improved the likelihood of power wheelies a tiny bit. I didn't notice a bit hit in mileage, if any real difference.
JM