Your engine is only 9:1 compression so it isn't going to run better on anything higher than 87 which is most likely the recommended octane by Honda. So 89 octane and higher is a waste of money. Several factors effect fuel economy Riding habits, tire inflation, riding environment, engine tuning, air cleaner, plugs, etc. one thing for sure mileage from 40-42 to 30 definitely isn't a fuel issue. It's a bike issue or a rider issue or both. 10% ethanol fuel has blamed for as much as a 10% reduction in fuel economy . I have not seen that reduction though. Still at 10% you should still be in the high 30's running 87 10% ethanol in the bike.