Jeff,
I meant to say some aircraft,not so A/C!
IIRC the 152 has a 3 stage blower,it might be a 2 speed 3 stage unit but I'm going off memory.
Look at the ATA setting at that alt,I bet it's much lower than say at 25K. Most planes cant fly in that rare air but even the P47 will show you reduced MAP and fuel consumption when you fly at those alts.
I'm sure if you search you can find fuel comsumption rates for the Jumo 213E.