What you're really interested in is cylinder pressures. You want to calculater Cold Cranking Pressure (AKA- Dynamic Compression). For pump gas, you want to keep the pressure below about 190psi or so.
Static compression ratio is part of the equation - but only part of it. You're also interested in intake valve closing point, altitude, and a couple of other things.
RB Racing has a nifty calculater for this. It's a harley site, but the calculater works for nearly any engine.
http://www.rbracing-rsr.com/comprAdvHD.htm
A good racing cam will also increase cylinder pressures as the rpm's rise. Even though the engine will run pretty good on pump gas, you'll need true racing gas for the track.
Aluminum heads can withstand higher pressures because they're better at transferring heat through to the coolant. Excess heat will increase detonation.