Never used anything other than standard unleaded in the Fiesta.
Never had an issue with it.
This should help with decisions;
http://thenewdaily.com.au/life/2014/...l-waste-money/
Don't get me wrong. I am not anti premium. Used to have a Eunos 800 Miller Cycle Supercharged V6 that specified 98. This was in the early days of premium and I got caught short coming back from Healesville once and had to chuck $10 worth of unleaded in as premium was no where to be found.
You can certainly tell the difference with cars that are tuned for it. But that's where the advantages start and finish.