I'd recommend the Fister mod (same as Pedro bypass, beautiful welding). Done to my S, no drone in cabin with top up, not too loud, but definitely rips at 5K+. Several compliments. I drove my Box in at 10, and picked it up at 4, about $380 with labor. He's in East SF Bay area.
http://www.fdmotorsports.net/index_files/Page441.htm