Yep, I have heard a lot of good things about Magnex. According to a large exhaust test Max Powe ran a few years ago, they were very high quality, and relatively quiet.
I had a cat replacement Mongoose on my EVO 6, and gained 17 bhp on the RR. But that is a different car, with a big blower on it. Noise wise it was great. Quiet on the cruise, sounded like a rally car when booting it.
As regards the performance gains on the 19 16v, they were marked. It had 138 bhp on the RR before, with a superchip, but unfortunately I didnt re-dyno it after fitment of the exhaust and filter( it was a straight-through, cat replacement system ), but the difference was very noticable. But then my car was incredibly tight and slow from the start, even the Superchips guys said so.
Thing is, people want different things from their pipes. The best thing to do is find someone with a car that is similar to your own and with a particular pipe fitted, test it out, and make up your opinion.