I'd keep it at no more than 12.5:1 static . I'm sure others would have run higher on 100LL, depending on camshaft, but if you have to back your timing off to avoid detonation with a higher CR, you will make less power than if you keep CR lower and have some good timing in it.
Of course cam size mostly determines what static CR you can run, not getting into chamber/piston shapes and quench. Work out your dynamic CR with the cam you want to run, with various different static CR's, and see where you at. I'd personally run up to a 9.5 dynamic CR on 100LL avgas. Keep your quench tight