I just swapped out a generic cone styled intake for a Monstaer Flow and can tell a marked difference in performance, but a small one.
The Roadster Sport 3 Muffler is what I am using and I looked at many units but really liked the sound of it...it's got a deep growl, however since I have bought mine I have a seen a few instances where people have bought the Roadster Sport 3 and claim the welds have given in places.
Might wanna look at long term reviews.
Also there are places where you can listen to the exhaust note of different mufflers but I forgot where I found it on the net, a search might yeild that info.
Happy Hunting!!