Compression ratio vs Porting

Hopefully a simple question. I'm only planning on very light porting of my 714 heads (late model 302's or early model magnums depending on who you ask) really just more clean up then porting.

As what point would a higher Compression Ratio be canceled out by the heads ability to breath?

As an example (using arbitrary CR numbers): if I upped my CR to 9.5 I'd feel hide power gains but would 10.5 feel any different than 9.5 based on the heads ability to breath?