TransAmVille, your exhaust is mandrel bent 2.5" stainless tubing. It'* been that way for a LONG time on the Bonnevilles. From the factory, we have a superior exhaust to the Grand Prix.
I can think of MAYBE 5 cars on this Forum that have 'outgrown' their pipe diameter or mufflers.
My exhaust is all Magnaflow now, but it started with a catalytic converter going south (replaced with a high-flow), which **** it'* guts into the muffler (replaced with an F-body Magnaflow), and then added a resonator so I could stand to drive the beast.
I'm flowing more through the motor than most SSEi'* here, and I wouldn't sacrifice my low-end for any exhaust in the world. My current exhaust flows perhaps 15% better than stock, primarily because I ported my exhaust manifolds and went with a high-flow cat.
We've had a couple cars go with 3" too soon, and they lost low-end.