Well the motor is rated from the company at a much higher MPG than even the 1.3L motor in my City.
Forget 3Stage for a moment, what about a VTEC-E head ? Thats lower power rated, but Im pretty sure its rated at almost the same MPG as the 3stage.
The 3stage makes more power indeed, but thats on higher revs thanks to VTEC.
I PMed a guy having a 3stage here n he can get around 13km/l widout A/C ... but on an AUTO CVT.