I just got my GS this summer and have started reading about motorcycles more. Two if my friends had sportbikes after high school, a R6 and CBR 600. Both of them got 50-55mpg. Since I have started reading about bikes recently I see that the newer 600s struggle to get 40mpg. Any Idea why? This could be my friends just rode more conservatively, but I think there is more to it then that.
The reason is the figures you gave aren't measured the same way. Your friends are riding nicely so they're getting good mileage. The magazines ride the bikes in city and highway conditions, and test the limits of the bikes on the dragstrip and tearing up canyon roads. Then they average it all together.
50-55mpg on a cbr 600 is easy but you have to keep rpm's under 6k. If they ride them like they were meant to be ridden then expect around 40-45mpg. GS500 average anywhere from 45-75mpg but I mean anything can alter numbers like gearing and rider. I did 210 miles 2 weeks ago 1 way on 3 gallons and I was going around 70-80mph on the interstate.