I don't haul mirrors to the shows with me so people can drool over the underside of my car. By "stockish" I only care about how it looks during a walk around or to the car behind - where it exits, correct looking tips, etc. A slightly larger pipe is barely noticeable to most people. If someone wants to crawl around looking under the car (and they have) then I suppose they can be disappointed.
Sound is less of an issue. I like a good, healthy sound from the exhaust but I'm not a big fan of loud and obnoxious.
That Comet sounds good. I always hated taking videos of running cars because the sound quality is generally horrible. Quieter is better since load noises tend to overload the mic and it just becomes a screech.