respectfully disagree with people that give out advice that you have 6 gears, use it, enjoy laggy turbo blah blah. sure i can imagine a bit of a wait being worth it if you're building up to 40psi / 500whp or something but when talking of relatively lower power with shortened power bands (band from 5000-7500rpm), not everyone is gonna find that fun to drive in any situation other than on track or the back streets. it is an amazing feeling when you have the space to push it and experience that sudden thrust, but you should really consider how much opportunity you have to enjoy that in your own regular driving conditions and whether sacrificing responsiveness to get a bit more top end power is really worth it.
in my personal tastes as a daily, the stock sti is such a sexy setup and any 'upgrade' should really be preserving the responsiveness/handling and building off that.