Sounds like a great plan, economy to meet the EPA MPG requirements, while you have the option to toss all that out and get massive amounts of power to Spin Tires On Pavement (STOP Principal!)
The Government is regulating us way to much! They even require that auto designers design out all knee room in new cars! Basically it is like this. Car manufactures must pass a crash test, and if there is space between the passengers and glove box or dash, then the dummy hits the dash hard enough to break the knees, so no knee room, the crash test results are better, and Congress has declared no knee room!
It just works that way.
If you tune a car to accept only 91 or 92 octane fuel, you can get much better mileage, yet will ping if you put in 87 octane again. As a side benefit, you also get more power!
But "Congress" has decided that there is absolutely no change in MPG when changing from 87 to 91 octane fuel (test it yourself your car might see a great improvement on 91 octane, mine did) so all tests must be in 87 octane, unless the manufacture declares the vehicle "Premium fuel only" and then it can be used.
With a $0.20 per gallon price difference, I have found that my MPG went up about 10% while fuel cost (at least while at $4 a gallon last summer) only went up about 5%. Now it is more break even, with fuel and MPG going up about 10%.
Fred.