Mike, the more of a compression ratio you run, the more octane it will need. A larger cam will bleed off some compression and reduce the octane requirement to a degree. Limiting total timing will allow a higher ratio but will cause a power loss.
I myself run a 11-1 - 360 engine with aluminum heads. The cam is a fairy stout one. The smallest I have run is a Purple 292/.509. It has 248*'s of duration at .050. I have not run a smaller cam with this combo. But this runs well on 93 octane. Your results may vary with the grade of available fuel, quality and where you live. (FWIW) I'm a few feet above sea level.
