I heard a bit from the Car Talk brothers (I regularly listen to their radio show on NPR), they said we should not be concerned about which grade of gasoline to use in our vehicles. Here is a summary of my research on the subject:
The engine of each car type is design to ignite the gasoline at a particular pressure, and the grade of gasoline relates to timing that ignition. Incorrect timing can result in carbon build up in the engine, reducing fuel efficiency, and potential long term damage. In general, the higher octane gasoline provides improved engine power and are appropriate for high performance vehicles. It’s generally accepted that you should follow the recommendation of the owner’s manual for your vehicle for octane ratings, and that using higher octane gasoline than the recommendation will not provide increased benefit to your engine.
According to this note by the Car Talk brothers on their website, scroll down to the section titled “Tip – Use of Regular Gas instead of Premium” modern cars have a sensor to time the fuel ignition, preventing the risk of damage to the engine. They also say this theory is controversial and unproven but that the risk may be worth the savings.
As a secondary note, choosing the brand of gasoline also has an impact on vehicle performance. The critical difference is the type of detergents used by Name Brand vs. El-Cheapo manufacturers. Auto manufacturers will recommend using Name Brand gasoline. The Car Talk guys also answer this question summarizing that sometimes using El-Cheapo, up to every other fill-up, is probably acceptable.
As a side note, gas stations near the highway are often more expensive than other locations of the same brand.