You are close to the max, which is around 90mpg. Wound out on the highway, into a headwind with 100 lbs. of gear on the rack, I'd be happy with 50!
I generally figure from 100 to 125 miles to a dry stock tank, 70 to 90 before hitting reserve. With stock gearing, 35 to 45 in 5th will produce the best mileage. Unfortunately, we don't have any flat terrain here in Hailey.