I have a pair of Flowmaster 40 series.... on my V8.... which is where they belong. They sound decent but suck performance-wise. Will be getting Magnaflows soon to replace them.
And yes, any chambered muffler will sound like a** on a 3800. I would just go for a stock replacement right now if you plan on switching to Borlas at some point. Depending on how bad the hole in your existing muffler is I would just patch it an move on.
Do a quick search for "mufflers" and see what is recommended.