I have been using 89 octane in a 350 with 11:1 forged pistons, 041-64cc heads,
after market HEI distributer and a Crane Hi 6 ignition. It has never pinged. Tried 87 octane, doesn't run so good. 91 or 92 octane made no noticable difference except to my wallet. Might be I just got lucky with the combination. Engines about 5-6 years old now.