long tubes ftw! Im polishing up my set of PI heads (only exhaust of course) and im port matching the intake, but you should do the PI swap, i did the cams, and it was great, now im going to finish it up! The long tubes are a bitch to install, i had to drop the whole K-member to get in there...
Your stock one will be fine, an aftermarket one will not net much hp, but if your set on one, get the JLT one, I've heard nothing but good news about it!
heres some info that might be helpful
http://www.jlttruecoldair.com/dynoresults.php
the only thing i heard good about it was that it prevents "carbon build-up" in the intake side of the engine, but i haven't seen any real proof of that yet...