The perforated Oem. exhaust mod. is about 20 % louder than stock .
This in combination with test pipes will sound more rasp .
The advantage of test pipes in combination with a tune is + 12-15 HP .
The downside of test pipes is drone , if you don't like drone...don't do it and keep it with the Oem. exhaust mod .
I have the Oem. exhaust mod for 2 years now and it's still jaw dropping with 0 drone .
Here is mine with pics and DIY video =>
http://www.m3post.com/forums/showthread.php?t=733817