Here's what the best Spitfire book (Morgan/Shacklady: Spitfire, the History), by far, has to say on the question.
Take note that it very well mentions the supply problems with the import of 100 octane from overseas, and also take note Glider is very well aware of this work, having shown this several times. Instead, he sells a story about 'hundreds' of books not mentioning a thing..
The relative lifespan of the engine (10-20 hours on +12 lbs vs 100 hours on +6 1/4 lbs) is also of interest.
