My 68 Caddy's 472 cranks around 185 average, and hauls a 6000lb rig around with no issues on 94. Friends ov mine have gotten away with 195ish on pump gas, no issues while running it, but one guy did have a few ugly surprises when he finally tore it down. On the other hand, my bone stock 76 440 with its 3:1 compression wont run on anything less than 91 octane without detonation you can hear, and runs WAY better on 94 than 91. WAY too many variables to pin an exact number, even on a forum that deals largely with a LOT ov very similar combos.

For what its worth, and completely apples to oranges i realize... but the N/A 2L VTec S2000 4-popper cranks about 230 average on pump gas... thats 11:1. They also make a 11.7:1 version that runs well on pump gas as well. (!!!)