AKI or "octane" is a valid test for detonation resistance valid for all. For maximum economy you want to run as high a compression ratio as possible without detonation, and not just use sloppy over rich jetting to protect the engine, but good spark advance control. LP is different in that you need to run in a narrower band of mixtures for it to light off. Misfire can be more of a problem if its not set up correctly.