I've dropped the extra coin on 89 here in SoCal when we were having 100 degree temps each day my way in late July through August. And am now back to 87 octane. If I knew I was going to take the car on a 110 + run I would run 91, which is the highest available here in California. The higher the octane generally has a less chemical energy than the 87 as they doctor it with ethanol to increase the rating, but even so, if the car starts pulling timing with the 87 gas then one is still better off with the higher ethanol spiked fuel. In a perfect world, given high outside temps, and a heavy foot, one would want me thinks a 95 octane rated fuel spiked with toluene or xylene, just as insurance against detonation, or the car pulling timing to prevent same.
