Personally, I wouldn't 'trust' the higher octane levels at the pump. Between how quick gas goes bad nowadays, and how few people buy the upper grades, is the gas any good by the time you come along and buy it?
While I 'only' have a stock '77 440 out of a NY'er in my wagon, when I first swapped it in, darn near everyone told me, regardless of year, big blocks need the higher octane. So, that's what I did. One day I found myself at a station that had ONLY 87 octane. Being on fumes and not sure how far to the next station, I put 10 gallons in, expecting the worse.
Much to my surprise, the engine seemed to run better and it didn't ping at all when I stuffed my foot into it which I was getting with 93 octane. Hmmmmm.
Thinking maybe it was a fluke, I switched back and forth over several tanks, and the results were always the same. I ran 87 all the time after that.
All I could figure was the upper grades had been sitting awhile and possibly 'bad'. Whereas 87 is constantly being renewed since everyone buys that.