Ah grasshopper, you have finally created a thread for a topic that has needed addressing for a long time.
The ultimate answer is BALANCE. The ultimate goal is to balance 'perfect' ignition timing with the highest CR your motor can support without knock. Since knock tendency changes dependent on load and RPM, CR tends to ultimately be a compromise to the highest static CR a motor can support, within the range of an acceptable ignition curve across the entire RPM band.
The rules of thumb of 9.5:1 for single plugs and 10.5:1 for twin plugs are the tried and true specs for a Porsche with a programmed ignition curve (whether it be vacuum or some other advance mechanism). Load is the biggest bugaboo that leads to necessary conservatism, since loaded motors knock more readily.
This is why knock detection is the key to running higher CR. You can be less conservative on static CR, since the motor can detect transient knock and adjust the ignition curve in the short bursts of knock in on the fly in loaded states. Thus, you end up with a more dynamic ignition curve and can thus run higher static CR with these sensors.
Cam choice and overlap/VE are also important elements, but that is a deeper discussion.
Net-net, optimal ignition timing will always pay more dividends than artificially high CR band-aided with crappy ignition timing.