MPG build 360
In my opinion we're talking a lot about the small things and a little about the big things. Sure there may be a difference between one OEM cam or another but you aren't talking huge difference.
Lower gears, lower displacement, raise compression, get the tune right, select components that maximize torque output over a usable RPM range, make it lean as possible during cruise and idle. Above all keep your foot out of it. These are the big things.