You're looking at it wrong. I can run my 16G at 4k without building boost. Boost is not necessarily rpm dependent. It is more throttle dependent. When you hear someone speak of these numbers, this is at full throttle. You wouldn't be flooring it or even half way flooring it once you are cruising. So the gas mileage becomes unaffected at cruising speeds. If you are slowing down/speeding up a lot you will suck down gas.
