Blouch TD05H-18GXT-R Billet Ball Bearing Turbo 8cm^2 Subaru Models (inc. 2002-2007 WRX / 2004-2012 STI)
Investing in a larger turbo as well as supporting mods is one of the best power upgrades you could buy. Blouch is the leader in turbo development, they consistently build the best turbos. The new XT-R line of turbos from them consist of a billet compressor wheel to optimize the aerodynamics of a turbo and increase compressor flow within the same inducer geometry. Which allows you to build more horsepower at lower boost pressure.
It also consists of a 43 lb/min fully machined billet compressor wheel, a high efficiency Garrett GT turbine wheel, Garrett GT full ball bearing system, and a 8cm^2 bolt on turbine housing.