Yeah, the subject has been brought up a couple times at least..
Try sentra.net. Specifically read the engine article in Kojima's Garage. Also try NissanPerformanceMag.com. Both sites have info about exhausts for the GA16DE. Also make use of the search button at the top of this page to search through old posts.
Nissan Forums is the go to place to talk about your favorite Nissan model, including the Rogue, Maxima, Altima and even sports cars like the 370Z and 200SX.