I'm new to Cats and bought a 09 M8 out of a crate last spring. I was fortunate enough to have my dealer put a SLP single on my sled before I bought it. I was so impressed with the way it works (and sounds) with just the pipe, that I went ahead an added their entire performance edition kit. I can hardly wait to try it out this winter.
By the way, the horsepower rating is 169.4 but, I was told that is a very conservative horse power number by SLP and that this was the lowest horse power number they got on the dyno of at least 20 power runs. They state this number because they want to make very sure that every sled they put out has at least the minimum advertised horse power they claim. Most sleds should make several more horse power than SLP's claimed minimum horsepower rating.