Ok, so I have a Gt35R on my 2004 STi. I have the tial 44mm external wastegate being controlled by an apexi AVC-R (1.3 bar/~19 psi target boost). I recently changed from venting back into the exhaust, to venting straight to atmosphere and I seemd to have picked up quite a bit of power, and a quicker spool up. So I think what has happend is that at some point my exhaust was becoming restrictive, so now that I'm venting to atmosphere i basically have 2 exhaust pipes and the flow against the turbine side of my turbo is better. Does that make any sense?

 

makes perfect sense, not to mention an open dump sounds badass!