Octane requirement question

And remember this the octane requirement varies with load and rpm and altitude. If you drive like I often do now that I'm semi-retired, you might get away with 70 octane. If you're pulling a trailer, and need to really hoof it, maybe you do need 91.

I would try the lowest scum gas I could find and,on an empty tank, try 5 or 10 gallons of it to see what I could get away with. If it gets into detonation, I would add an equal amount of 91 to arrive at an octane somewhere close to half way in-between . If it doesn't detonate on the scum, I'd run it. If it only occasionally detonates on it, I would keep track of the circumstances, and if it works out, perhaps a slight timing change to either the amount or the rate will fix it right up.
Typically, on a non-computerized vehicle, an octane change will not significantly change power output, so long as detonation is not encountered.
If you're gonna drag a moose outta the bush, at lower rpms, and large throttle openings,Use low range and listen hard for detonation, or just run the good stuff. But honestly 4 octane points at 4000 ft, at 150 psi,I can't see it being a problem.At all.