91 is all I've ever put in. The dealer gave me Petro Canada gas card when I bought the car. Once it's used up I'll be going to Canadian Tire, their price is always better then Petro Canada.
The manual aka GM specifies to "Use premium unleaded gasoline with a posted octane rating of 91 or higher" and recommend Top Tier Detergent gasoline be used (page 9-51). So yes, 91 is all you need to keep your Stingray and you happy.