Nick, your statement that motorists are trained to think is misleading. I don't believe they are trained to think at all judging by the standards of driving nowdays.
With BMW,s using an adjusted version of the old Toyota advert, "the car that has to be in front", Audis full of BMW drivers who realise that the BMW is now "as common as a Cortina", another saying from back in the day.
Volvo drivers have always been on another planet, drivers of French cars angry that they have not got something better, Mercedes have a greater proportion of older drivers, some who should not have a licence so no change with them
But, going back to the original thread, My old Senator 3.0S used leaded fuel.
When I had to change to unleaded, I used Castrol valve master as a lead additive.
My MPG dropped to 23. Shortly after, Castrol brought out the additive with octane boost. Using that put me back to 30 MPG