OK, its weird
The Bosch Blue coil is supposed to be ballasted. However, when I turn on my ignition (car not running), the voltage is still 11.67 volts. It does show a 3-4 ohm resistance when I test the primary resistance at rest
Is that a symptom of a busted coil? Perhaps the internal ballast resistor breaks down at high revs.
I will swap in a spare coil (that just so happens to be not ballasted) and go for a short drive. If it can rev properly, then I will get either another ballasted coil or an external ballast (as replacing ballasted coils is expensive).