Motorcycles

I don't think it's true that lower octane burns faster or that aging results in less energy, though results from a search are conflicting. The important factor of octane is knock resistance, tendency against igniting before the spark in a high pressure environment - for example wide open throttle on a hot day in a high compression ratio engine. Degradation from sitting isn't that serious in the short term for OP's purposes.

Iso or better yet methanol is good to absorb and burn off water in the tank but you don't want water in there in the first place. It will leave deposits in the fuel system that clog things up, and can start the tank rusting. Better to avoid in the first place by riding the bike regularly to keep the gas fresh and checking the tank ring drain of a bike sitting outside once in a while to make sure it's clear of grime. Passive water absorption is a thing too but less of a concern over a timeframe of months.