factory vs aftermarket cat back exhaust

[bodes-sh]

im just wondering what differences people have noticed in fitting a 2.5" cat back to an AU I6. Im thinking that there wouldnt be much difference over the factory 2.25" apart from having 1 or no mufflers.

so if you could post what brand it is and what the difference was, im trying to get an idea for going full system or cat back and trying to decide on 2.5" or 3".

Thanks
Bodie