Tonight I had to put some 98 Octane fuel in my 659cc 2004 Copen (95 wasn't available where I was). Am I imagining it, or is the car totally different on 98??? The drive home was like being strapped to something else altogether!! I had a friend who always claimed that 98, although more pricey, actually ended up being more efficient and cheaper in the long run. Anyone who's done some actual stats care to confirm?