In my world pinking refers to a meeting of pressure fronts...the fuel is not being ignited without the spark plug....retarding the timing will prevent pinking.
I did not realise that the engine in question has unadjustable ign. timing....I must stop posting in US car threads eh? Sorry.
I would be thinking more along the lines of fuel mixture (check will also show faulty EGR) and engine temperature if it should be capable of running that octane fuel.