Race gas vs pump gas on lower compression street/strip motor

higher octane fuel has less BTU per lb than regular fuel, but it resists knocking so you can use higher compression to extract more power from it, but it wont help a 'normal' engine. Propane has even less but its octane rating is like 130 so you can run 13:1 and extend the duty cycle of the injectors to get it up to gas specs and higher. My SC required 93 'use premium only' on filler cap, and I can tell the MPG's are lower using cheap. I think the computer manipulates the spark advance on the fuel grade. Got a Flex-fuel Caravan and the MPG sucks on E10 but its cheap, 2.97 here in CA.