I've done the oem STI VF35,VF34 single scroll & VF37 Twinscroll conversion and Its not worth it imo(in terms of what you need to buy $$$ to do the conversion)
but I hate the subie rumble love the TS noise tho coop with straight pipes
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You will net similar results around 275-280hp(hub) and around 400nm torque
Only thing is that TS will give you more low down torque and a slightly faster spool up but the VF35 with the oem P15 housing should spool the same?
If not a wrx TD04 with 2bars should do it.
Get a Verso tune with 26spi and a forge actuator then bulk suspension works dont worry about the rims. OEM FTW