Use premium. Given the cars compression ratio, it does matter. If you want optimal performance and fuel efficiency, you will use premium. Its my understanding that regular will not hurt your car, but your car's computer will have to readjust to make up for the lower octane so that it doesn't ping, and that will lead to lower fuel efficiency and less power. This is all information I've been told by reliable sources over the years (articles online, Car Talk, etc), though I myself am not a mechanic.