I see you've already ordered them, but I just wanted to mention that it depends on what model and year of Sirrus you have. In 2009, the base all-aluminum Sirrus has plenty of clearance - I would say you could go 35c easily. But the next up Sirrus with carbon on it has tighter clearance in the rear - there's some more room between the 28c tires it comes stock with and I think there's plenty of room for a 32c tire assuming you don't also have fenders on there (maybe there's room with fenders, just not sure).