check out some of these exhausts...we were tired of this question on the forums so we decided to get a bunch of IS's together and at the EOS meet a couple of years back we ran a bunch of exhausts...click the "i6 exhaust competition"
http://lgwnorcal.com/videos.shtml
the fact is your taste and my taste is different. so what I think sounds, looks and performs well (apexi N1 full cat back...not in the video), you may not like.
rolo