My 406" LA iron-head Duster with 214/224 @ .050 and .470/.504 was 9.5:1 real CR and it was at the edge of detonation on Calif 91. I pulled some timing out to be safe. Still ran well (street car), but never hit the track to compare ET/MPH. Stock converter, 3.21 gear (9.25 axle), 28" tire, guess about 3400 lbs.
Elevation, duration & overlap will lessen that a bit as each increases, but it's way better to play it safe than to rattle the thing.