¡Ay, caramba! This diatribe tells me you have no clue what you are talking about.
Premium doesn't resist detonation by being less volatile or burning slower. That is just a simpleton trying to rationalize with simple concepts that he
can understand but have no basis in reality.
Even the most basic of concepts of octane ratings you get absolutely wrong. For you folks down under, Kia doesn't recommend 91, since your octane ratings at the pump are denoted in RON (Research Octane Number), same as in Europe. Here's the exact verbiage:
"For the optimal vehicle performance, we recommend you to use unleaded petrol with an octane rating of RON (Research Octane Number) 95 / AKI (Anti Knock Index) 91 or higher. You may use unleaded petrol with an octane rating of RON 91~94 / AKI 87~90 but it may result in slight performance reduction of the vehicle. (Do not use methanol blended fuels.)"
Source:
https://www.kia.com/content/dam/kwcms/au/en/files/owners-manual/kia-stinger-owners-manual.pdf
Here in USA and Canada, our pump numbers are in AKI (Anti Knock Index), which is (RON+MON)/2.
FWIW, 91 RON is equivalent to AKI 87. 95 RON is equivalent to AKI 91. So for Australia, Kia's recommendation
is for premium 95 RON gasoline, for optimum performance.
Now then, is premium gasoline absolutely necessary all the time? Of course not. Octane requirement for any engine is not a constant number. It varies depending on how the car is driven and under what (vehicular & ambient) conditions. WOT uphill in 105F Summer heat fully loaded with passengers and cargo, towing a heavy trailer near sea level has an octane requirement very different than, say, flat hwy cruising solo in Winter at steady 55mph in mile-high Denver. Kia doesn't know exactly how every driver of their cars will do, so their recommendation covers the worse case scenario. It is contingent upon the driver/owner to pump what is expected of the car for the next tank full.
I personally have no problem pumping regular grade, if I'm just commuting and taking it easy in cool weather. However, for track day or AutoX, especially in hot and humid Texas Summers, you bet I'll make sure the tank has nothing but the highest grade pump gas. Maybe with a few gallons of E85 added for good measure.
But, you - like all of us - are free to pump whatever you want into your own cars.
Just don't talk out of your behind on subject matter you barely have a rudimentary understanding.