This chart seems very conservative. There are lots of people running higher effective CRs per octane rating than this table shows. I bet it was published back in the day for overhead valve or even flat head engines w/o fuel injection. Back then you needed a lot of safety margin to keep it from blowing up. Combustion chamber shapes have improved a great deal since then, and are less prone to detonation. More importantly, with Fuel injection you can (with proper tune) run much closer to the extreme power ideal w/o crossing over into destructive A/F ratios.