Are you in europe? In europe, mainly the UK, premium gas is 98 RON. (research octane number). In the US we usually determine the octane by using a formula with the RON and MON and call it AKI or "anti knock index". So 98 RON gas is similar to 93 US gas IIRC.
If this is US, 98 AKI gas, I wouldnt run it in a malibu. There will be no benefit on a stock car, thats approaching race case octane. Octane is resistance to detonation. In cars made for 87 AKI octane, running premium can lead to deposit formation with long term use, even thought millions of american sheeple thing running a tank of premium will "clean er' out". Which is a myth.
If you are in the UK, or europe, and you are talking about 98 RON gas, that would be similar to US premium. If the car doesnt recommend or require premium, dont run it! Unless you have a way to get it super cheap or free......
I do believe there is some correlation between octane and head temperatures though.