i think that is why most of us are waiting to do mods.i know thats
my reason for waiting.i don't want any ill effects from tuning.
i'm waiting until i have as many choices as the wrx owners
UTEC,EMS,Unichip,ECUtek when any or more are ready thats when my pockets are gonna be empty,ha,ha
i've heard with only minor mods the boost can be as high as 17.5
without any engine management
if it was me i would put the catback on and sit tight for eng. man.
I personally think that a EBC like the Apexi AVC-R where you can set the boost duty cycles to different values for EACH gear would be on of the better solutions to this problem. I don't think anyone has tried it but it would be worth a shot. I think there has been some success with the deadbolt port-n-polish VF39 mod but other than that I don't know. Personally I live at high altitude so I will take all the boost I can get (up to 18psi or so) and my STi will just then be flowing as much air through the engine as a stock sea level STi.
Another thing to try would be to run with the stock muffler on and see if that works. If that doesn't then maybe try the stock downpipe with the perrin catback.
Take off exhaust and just use downpipe. IT is best power gain without running into boost creep problems. If you want to use the exhaust and downpipe you'll have to port the turbo wastegate outlet. It solves the issue but some people get a little antsy doing this. I do it for many cars and if you bring in the turbo only takes about an hour.