Just a thought- if you want more power you can get a turbo. Choose appropriately and it will work out for both gas mileage and power. You will NOT get better mileage when under boost, but you can still get good mileage when not boosting, and have plenty of power to boot. My turbo starts spooling around 3,000 so if I want to retain my mileage it's very possible.
When not under boost, assuming you are fully tuned, you can retain the same mileage as if you were not boosted. Then you can hit the throttle and gain an extra hundred horsepower, or more.