I keep reading threads were people talk about back pressure being good or neccisary for low end etc. Here is a link to some articles on exhaust systems from NissanPerformanceMag.org. I think these article do a good job of explaining back pressure etc.

http://www.nissanperformancemag.com/...fthenerds2.php

http://www.nissanperformancemag.com/...revenge_nerds/

 

This question was addressed in the FAQ a llloooonnnggg time ago.

Thanks for the new links though.