[bombcar]

High octane does NOT increase total available power, in fact it reduces it.

It enables higher compression so you can get more power per unit of engine weight, but the fuel efficiency per gallon is lower.

And the lead is for the valves.

You can get more efficient planes but you can’t overcome the need to fight gravity at some point.

[cma]

I thought higher octane improved efficiency by avoiding premature combustion, but that may have only been relevant before electronic fuel injection.