This is what I think you should do. Get a Cobb Accessport and a TBE (downpipe and catback). Dont get the TBE without some sort of EM (engine management) or you might get boost creep. When you get the Cobb Accessport and TBE you can go to a Stage 2 map. You should notice a nice gain in power and torque especially if you get a protune after.
BTW I recommend the Cobb Accessport. I know alot of WRX/STi guys running this EM and they have nothing bad to say about it. Its one of the best out there.
If you need more info go to
www.nasioc.com. Just search and you can find anything you need there.