I had an '82 Honda 450 Nighthawk when the nationwide speed limit was still 55. With a clear "PlexiFairing" on the front, I could consistently get 75 mpg. However, it's top speed was only about 70 with that fairing.
Then a few years later, when the speed limit was 65 on the interstates, I tried to take a trip, and had a lot of difficulty just maintining 65 (with a passenger), and my mileage plummeted. As I recall, I was getting in the 40's and was horrified. It wasn't until later it dawned on me that I was basically running that poor bike "flat-out" on that trip. No wonder it's mileage stank.
So from that experience, I'd say yes - "pushing" a small(er) bike to the limits of it's ability could very easily backfire. Of course, if you just drove slower..... If I'd kept it down to just 60 on that trip instead of 65, I'll bet things would have been a lot different.
It was a nice bike, but eventually I decided bikes weren't for me. It was actually my first attempt at a "super high mileage vehicle". Now, all these years later, I have my second attempt - my Suzuki Swift "White Gnat".
