I'm guessing that the S motor will require premium because of the turbo, the non turbo motors recommend premium.
Regardless, if you use regular fuel, the computers in both motors will adjust as much as it can to prevent spark knock. That adjustment usually results in slightly lower power and sometimes even a tick or two lower MPG.
Since the motor is small and performance oriented, you might be better off on midgrade fuel. Though you might want to consider a vehicle that doesn't require/recommend premium if you don't want to use premium.