To be honest i doubt there is much noticable BHP difference between the systems, especially if there all the same size bore with similar straight through rear silencers.

I think magnex have the best looking tail pipe though!!!

Have you thought of a custom exhaust system ?? then you get exactly what you want in terms of fit and sound. My mate had one done and they can tune the sound at different rpm, ie if you want it to be loud at idle but quite during motorway crusin they can supposidly do it !!