I gotta dis-agree with you, Feets. You will never see bsfc numbers in the .4s with any turbo engine(with the exception of direct injected engines). It's not all that uncommon to see .45 in a well thought out n/a engine.
The myth of economy with a turbo engine comes from, as previously stated, a smaller engine that is capable of making the hp of a larger engine. If you were to use that smaller engine in boost all the time though, you would be no further ahead in economy. It's the time out of boost with a smaller engine that you see your gains in economy.