can 1 octane make this much difference?

Just got home from the All Chrysler in Carlisle. Drove the 68 Barracuda. 250 miles each way. My 340 10.5:1 compression has never knocked but I have always run 93 Octane in it. On the way home I stopped for a fill up and selected the highest octane. Just as I was squeezing the handle I noticed it was 92 Octane. I thought, what can 1 octane matter. I put 11 gals in a 18 gal tank. I drive about 2 miles and hit the on ramp. I stick my foot about 1/2 way into it and the ole 340 really rattles. The rest of the way home, everytime I try to give her a good load, I detect a ping. Had to lay off her the rest of the way. I don't think 1 octane could make that much difference. My guess is somebody selling 87 for the price of 92. Any opinions here???