whats the best engine for both performance and mileage??

back to the original question......mileage with power is a turbo'd engine, maybe a 4.7/545 combo with a turbo on it? If you run a "dinosaur" la engine, a 273 with a turbo would get you mileage with 300 hp. One thing that helps is to reduce internal friction as much as possible, narrow rings with low tension oil rings. Just some thoughts.....