Exhaust valve color

What's your cranking cylinder pressure?

I ask because,...your engine only needs enough octane to prevent detonation under load.
An engine might need 93 at WOT, at a certain rpm, but only 91 at other times, and can be quite happy cruising on 70, and burning 87E10 at Part throttle.
Sometimes, delaying your all in by 200 to 400 rpm, or pulling it back 2* is all it takes to reduce your engine's octane requirement, to something a lot more affordable;
Jus saying.