Note: these examples are all from May 1940.
Here's an example of 12lb boost at low altitude:
here's another:
http://www.wwiiaircraftperformance.o...e/bushell.html
note here that the pilot is using "full" 12lb boost and he has noted that he was at 5000-6000ft.
and another:
http://www.wwiiaircraftperformance.o...e/bushell.html
again at 5 -6000ft and again with 'full' 12lb boost
The idea that that they were using 12lb boost with 87 octane fuel could only be conceived by someone who desperately wants to avoid the truth.