i put a wideband o2 sensor on my stock ecu and it ran 11.x-1 on full load, and about 13.x-1 on light load (normal driving).
why would you sit longer in the higher gear? if you mean that you are at full throttle but not fully on boost, you are still running richer than you would at less throttle %. if i am driving along and accelerate from 30kmh to 60kmh, then just cruise in 2nd gear, then lean out the mixtures and do the same thing again, the second time i am going to accelerate faster due to having more power, use less fuel due to leaner mixtures, and spend less time at 100% throttle and more time at light throttle. light load at higher rpm uses a lot less fuel than full load at a lower rpm.
if you are running 5psi and if you can sit at 5% throttle at 6000rpm (off boost), you are probably going to use less fuel than 3000rpm at 100% throttle (and full boost), as the amount of air going into the motor on each stroke is probably about 10% of what it is at full boost, so about 10% of the fuel is needed to have the same afr. now those figures of 10% may not be accurate, but it would be in the ball park.