This is as close to trolling as Jasmine gets 😄 when we can figure out how to deliver it we will award Jasmine with the annual "Slowest Compass Driver" award!
That's basically what it boils down to, your average speed for your typical driving.
I don't think it's so much the speed as it is the acceleration. BMW did a study in the 1990s and concluded that the best fuel economy resulted from moderate acceleration to cruising speed -- neither slow nor quick, but deliberate.
I've done a few "studies" of my own and I learned that my LRR easily tires deliver about 10% better fuel economy than my snow tires. Winter/summer temperatures account for another 10%. The ideal speed seems to be in the low 60sMPH regardless of tires or temperature.
So using my vehicle as an example: (Using my EVIC that seems quite consistent with actual calculations)
I get 38MPG between 55-65MPH at 70F with LRR tires. Approx 250 mile trip.
I get 32MPG between 55-65MPH at 40F with snow tires. Approx 250 mile trip.
My record is 38MPG at 65MPH at 70F with LRR tires. Exactly 290.7 mile trip.
My impression is that people who drive 70MPH and are often accelerating to 75-80 to get ahead of other drivers and probably waste 20%, excluding other factors. They're using lower gears to accomplish the same speed they could have accomplished in a higher gear, plus the extra fuel in the process of acceleration. They'd probably do better at a constant 75MPH than they would vacillating between 70-80. If they're driving aggressively in the city where their MPG is going to be lower because they are always in lower gears, they're losing that 20% based on a lower number to start with, so yeah, they're probably only getting low to mid 20sMPG. It's not the vehicle's fault, it's how they drive.
People who drive aggressively don't always realize it. I knew a girl in college who said, "I don't drive fast; just so I'm passing everybody." My dear, that means you're the fastest car on the road!!! It never dawned on her. And yes, I said she was in college, so certainly not stupid on some level, but clearly lacking self awareness.
Finally, in my first 10 years of driving I endured two oil embargoes and the resulting gasoline shortages. In those days I wasn't so much worrying about the cost of my fuel as I was worrying about even being able to buy gas when I needed it. I necessarily formed good habits.
End of rant.