David Vizard's book "how to build Horsepower" had an inverted triangle chart that gave you the 'order of magnitude' from old to new CR...I have it somewhere but from say (for example) 9 to 11 was much higher percentage than from 11 to 13 which to some extent is mathematical 11/9ths is a higher proportional increase than 13/11ths. The higher you went the lower the gain, while it's true as you increase the pressure you also increase the speed of the flame travel, but at some point you hit diminishing returns and design limits of the engine itself.