HKS Hi-Power Cat-Back Exhaust with Titanium Tip for Mazda RX8 (Series 1 & 2, 2003-2012)
I'm running it with the stock cat, and it's relatively loud, but not obnoxious. I haven't heard it compared to the borla though. My wife can hear me from about a quarter mile a way if she's outside and I get on it. At idle and just cruising, it's fairly tame. I haven't had any trouble with it or any unwanted attention. It is not raspy at all and doesn't bellow as much as say a Greddy SP2. It's actually only a tad louder than an SP2, so if you've heard one, you can get an idea for sound.