Dragonwind,
I recently added a Stebro Sport exhaust to my 986. So far I like it a lot.
RandallNeighbour's advice above is very good. My exhaust is noticeably louder in the cabin with the top up. With the top down the sound is either masked by wind noise or just doesn't resonate as much with the open top.
I'm really curious to hear what it sounds like with my hardtop installed.
ddb