[Henry Schmidt]

Cylinder pressure, ignition timing, fuel delivery and heat all effect the engines' tendency to detonate. Not to mention octane in ever decreasing amounts.
U.S. versions of the 80-83 911SC engine were prone to detonation with stock compression. 9.3:1. I don't know how many engines I've disassembled with broken pistons do to detonation.
Unless modifications are made to the fuel delivery system they will detonate over 9.5:1.
The problem seems to be a lean running condition at max torque (4600+- a few rpm). CIS injection will tend to go lean at cruise in most applications but when you throw a lambda control unit into the mix, lean is an understatement.

Lean running and high compression are a formula for disaster. The is why the W.O.W. (9.8:1, 210ph) engines have a special fuel distributor, warm up regulator, ignition distributor and no O2 sensor.