Miles or smiles?

Miles per gallon?
Yes, I care about that, somewhat.
After all, it can get expensive to run a car that is horribly inefficient.
But combining efficiency with excellent performance can be quite a balancing act.
My '13 Mustang, in its current state, gets 20 mpg when cruising on the highway, even more if I could keep myself from going faster than I should, and 20mpg is actually efficient when considering that the car's now producing approximately 700 horsepower.
Conversely, introducing the gas pedal to the floor under it produces rapid forward propulsion, leaving me with a huge smile on my face.
And that bring me to the "smiles per gallon" part.
A car's ability to produce lots of smiles per gallon ... now that's a rating that should be on every window sticker.