I may be able to help with a little info and some evidence.
Disclaimer:
Picture heavy post for evidence and all numbers are on an Australian dyno, because well, i'm Australian.
I run a no name (not nameless, i legit have no idea where it came from) DP with high flow cat and X-force the rest of the way back.
http://i.imgur.com/BPS1AHC.jpg
It's a long story involving shitty manufacturers services, misfires and boost leaks as to how i got to this point however i was overboosting like a boss! My mechanic spent a few hours checking things, changing things and looking for restrictiors etc all to no avail - She just wouldn't drop below 21psi and this is on wast gate.
http://i.imgur.com/JVuGzJL.jpg
Nath (mechanic), has done his fair share of Subies in his time and suggested boring out the exhaust housing - he's a close friend and a dope mechanic so obviously i told him to go ahead.
When we pulled the snail - i say "we" it was mostly him - we noticed that the actuator won't fully open because it's fouled by the housing so we hit it with the die grinder and removed the offending material (photo is pretty terrible because of the new shiny surface).
http://i.imgur.com/CkynfSw.jpg
http://i.imgur.com/JOXdHYe.jpg
http://i.imgur.com/4iqGGNC.jpg
Then proceeded to bore the housing because there is a gnarly lump in on the way to the waste gate.
http://i.imgur.com/kvbQOsJ.jpg
http://i.imgur.com/8udthBj.jpg
Back on the Dyno and it was manageable again. I can't remember the numbers off the top of my head - i want to say to 14psi - but Paul (tuner) said that they were where they should be on waste gate. Sadly i don't have a sheet for the waste gate only runs - sorry.
http://i.imgur.com/D4fb90M.jpg
She's running 16psi now with no problems - Pretty sure the sheet for this is in my car, i'll try to remember to grab a photo and chuck it up.