I splurged and went for the stainless muffler with a lifetime warranty.
Very happy with the results: The exhaust is tucked up snug & tight to the underbody, it doesn't rattle against anything, and the car purrs like a Rolls again.
I joked (half joked?) with the parts guy that there is probably a 0% chance that the company will still stock this particular muffler by the time I need to claim a warranty replacement. In another 10 or 15 years maybe?
We'll see. I'll post back when that happens.