There is an Aussie company called chiptorque that's sells a piggybag chip for the pre new impreza models. In combo with a bleed, you're able to run 1.2 bar safely with this chip. With a full open system you'll be able to get 270 HP and 370 Nm. Downside is that the turbo in the WRX is so small, there's no more ooomph after 4,000 RPM.
The EVO takes off at 3,500 RPM. Below that it feels more sluggish, but that is compensted by the different (shorter) gearing.
Don't know if the chip is available for the US. As for 227 HP... it appears that the US version is different. Therefore I don't know if Aussie or Euro ECU add on stuff will work reliable.
Check I-club (
www.i-club.com) for more info on the US model
Nico