Doesn't seem to be much advantage over stock for performance mufflers targeting the m42.
Ding Ding, hence my term "presents for your car". Anything that doesn't add any noticeable gains to your car are merely presents imo.
Obviously, if your motor is built already and the exhaust is the only bottleneck holding some good power back then that is where I can see an upgraded exhaust. But there seems to be only a handful of those so far.