I disagree, i have a 9.4:1 compression 340 and at the track, on a hot summer day, it would start to ping at the 1000 foot mark and go nuts by the 1/4 mile.
And thats with 91 octane, as high as you can get around here.
4400 feet elevation race track.
It only took one gal of 110 to a half a tank of 91 to rid the ping.
Cam and ign time take a hand in answering this question as well!
MP .474 280 cam, advance 4* and 36* total ign timing.
At 7000 feet above sea level, were i live now, I never need anything but 91 Pump Gas.