Higher octane is a waste of money. It is only for higher compression engines. If you experience knock, try another brand or the next grade, but you should not need it.
I have always used the least expensive gas 86 or 87 and mine nowadays has about 10% ethanol for smog reduction since MTBE is no longer used here.
That premium gas has probably cost you about a $1000 extra so far. That goes a long way to fix any repairs that may or may not ever happen.
311,000 miles on 4 cyl 92