If I were you I'd stick a set of good more aggressive pads in ( semi track pads) get some springs/coil overs fitted and go drive your car properly before worrying about a bigger turbo etc etc.

The new standard WRX is awesome and has enough power to get you into some trouble.
Being able to scoot it through a corner just as quick will upset more people :-)

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2016 Subaru Outback - Work Wagon
350NM of CVT Goodness
Pit Crew, shit talker.