Turbojimmy,
What I was attempting to say was the higher octane provides much longer time before goes bad. On avgas at the 100LL does infact last way over a year in a airplane fuel tank. Why I started using the good stuff in my gasoline engines, like the lawn mower can sit all winter and start & run in the spring like it was just shut down. Can not address why your 454 runs hotter on the better fuel, maybe timing is an issue?
I have converted all in my area using Speeders (rail car) guys to use the better gasoline for the small engines to operate so much better, better idle, start and overall operation. No more gummed up carbs from old gasoline etc.
I have spent 40 years enjoying small engines, how I got into the Onan generator world 40+ yrs ago.
Dave M