I wouldnt be surprised if you lost a few mpgs with the extra tall gearing.
If the motor is lugging and workig hard to stay up to speed due to being geared too tall you end up twisting the throttle further to maintian speed, compared to a motor thats running free at higher revs that takes very little throttle to maintian speed.
I had a couple guttless cars that got better mpgs in drive instead of od because they were lugging in od.
My 650 KLR also lost a couple of mpgs when I tried tall gearing on it, it didnt have enough power at low revs to pull 5th at less then 100km/h, revving the snot out of a motor doesnt hurt mpgs all thet much, trying to go 120 plus km/h does tho, its more about the speed you ride at not the revs.