I have a k-tec cat-back exhaust with mid silencer. It used to be boomy for the first 1000k miles around 3.5k -4k revs but has nicely settled in now. Sounds business like but not too loud. I have to keep to 98dBA for track use and without the mid silencer I couldnt achieve that. performance wise an exhaust on its own will not give you much, but it becomes important when added to other breathing improvements e.g induction, TB, head, cams, etc.
The quality of fitting and workmanship from K-tec was excellent.