My fuel flap decal says "Minimum 95 ron" I run 98. I have run 95 ron and the fuel economy is worse, so it works out similar cents/km.

I did run 91 once as the stupid dealer gave me a free tank of fuel as compensation for another stuff up. The difference in torque was unbelievable and fuel economy was affected by 15%.

We also run 98 in our 20yo mazda 323 as it goes 2-3 months between fills and fuel does lose octane as it ages.