There is more lead in 97. The lead is for the grease purpose of the engine. So generally more engine power needs better grease capacity from the petrol = higher octane. But nowadays there are other chemicals to add in order to obtain the same grease capacity of the petrol. You can always use higher octane then recommended but not lower. Just use what the manual states. So there is not more "power" or something like that in higher octane petrol. The engine will not become more strong.