Octane has nothing to do with fuel economy or giving more performance. Simple: If the manufacture calls for premium, then use that. If they don't, then go with regular.
Octane is a fuels resistance to Detonation. High Octane rating means that it takes a bit more for the fuel to ignite. That is important when a engine is designed for it (Higher compression ration or more advanced ignition curve). For example: Many outboards are identical except for the ECM programing. The higher horsepower motor has, among other things, an advanced spark curve along with more aggressive fuel mapping. This could lead to pre-ignition with regular fuel, so they call for Premium.