You've got your baseline -- now go for Stage 2. You're only a downpipe and tune away.
You aren't risking the longevity of any component at that point. Get a Tactrix cable and tune it yourself with RomRaider -- the STi is popular enough to have plenty of base maps available to have you running strong in 15 minutes.
You don't risk going off the deep end till you start thinking of a new turbo. Next thing you know you'll be in an AWD version of your last car.