My 406" LA motor - Duster, AT, 3.21 gear, AC, street car, iron heads - was right at the limit @ 9.5:1 measured static compression, on Calif 91 octane.
Cam was 214/224 @ .050, .470/.504 lift on 110 CL.
Had to pull timing out of it. Car ran great, though, and would pull 17MPG @ 70-75.
Aluminum heads would allow that CR and more.