My engines teacher told us that you should only run enough octane to keep it from spark knock... any more and you are just spending more money than you need to...
If it runs better on it, and you don't mind paying for it, then go ahead.
But you should tune it for the gas that you plan to run all the time. If you tune it for the good stuff and then put the cheap stuff in there, you may get some spark knock...
Than you would have to back off the timing a bit and then readjust the carb... Basically re-tuning it all over again...