No need to use 93 Octane in Spark (US Sparks)
I had used 93 Octane (or Premium) gasoline in my car for a while thinking it would be cleaner for it and the car's power had diminished as far as accelerating power goes. Well low and behold, by switching back to regular gasoline, my Spark is back at fast acceleration (I have a CAI and custom catback installed), and just feels smooth overall.
The 93 Octane is mainly used to reduce knock (pre-combusting) in higher horse powered vehicles or vehicles with a high compression rate. Regular unleaded is more than enough to get the job done and as long as you're using a top tier gasoline (ex. Valero, Exxon, BP, Shell), you'll be running cleaner due to their detergent additives.
Hope this helps some. I'm not a mechanic or anything, just a guy who knows his way or two around cars and shares what he learns from experience