I have no experience with boosted motors either, but a motor is typically most efficient at 80% load, rather than 80% throttle. You can tell you're at full load when you reach the point that pressing the pedal further doesn't accelerate you faster (or not much anyway - most motors start to enrich the mixture at some point and you get a bit more oomph).
To my knowledge, a turbo can actually increase FE because the motor is running at a higher compression, the only thing you might be fighting are fuel maps. You could read up on "pulse and glide" in Driver's Ed and try a tank using boost + that driving method, and see if it dramatically affects mileage.
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