The issue of premium vs regular gas has always been a controversial one. Oil companies have long claimed that their premium blends provide more power or efficiency than regular fuel. The problem is that real world results tend to be be very mixed. While it's true that using a higher octane fuel can allow an engine to generate more power and/or run more efficiently, the engines have to be calibrated to take advantage of these fuel properties. Many modern engines with sophisticated electronics are capable of doing this, but not all.
According to AutoCar one machine that does benefit is the Vauxhall Astra VXR. While Saturn dealers only get the normally aspirated 1.8L Astra, the VXR version gets a turbocharged 2.0L engine. In testing with premium and regular gasoline, the engine produced 17 hp on premium while also getting a mileage bump from 22 to 25 mpg (18.3 to 20.8 mpg (US)). Turbocharged engines like this definitely have an advantage because they can run higher boost levels compared to normally aspirated engines which have fewer parameters to adjust. The question is, does a 13 percent bump in efficiency outweigh the extra cost of the fuel and the extra energy to refine it? That question remains unanswered.