Andy RR your faith in catilytic converters is somewhat missplaced I think.
The only difference between 'leaded' fuels and 'unleaded' fuels is the addition of a
VERY small amount of TEL...it is very small because for decades now they have been putting toluene and all sorts of other carcinogens in all fuels so they could minimise TEL...even avgas has these ring compounds in
almost the same amounts as ULP
Seeing as how cat converters are so innefficient and, indeed, stop working after a relatively short time from new (a year or two-20 to 50000kms) I hardly think it is reasonable to suggest they are responsible, alone, for our cleaner air.
They are (or were), apparently, not mandated in NZ...and their air is at least as clean as ours.
Yet another example of single issue advocasy and political correctness robbing society of an informed decision I feel.