I think the OP just wants to know what it takes, not really do it.
If he wants to stay with 4 cyl turbos, I'd say ditch the subaru, and get a talon tsi or eclipse gsx and or evo and slap on a big turbo. you'll be @ 600 all day on 93 with the right turbo setup and some motor work
Listen to whatever Phatron has to say in regards to subarus..
but, for street use, point A to B, I think 300-350 whp is more then enough..
****, a stock 2.0 wrx is more then enough for just "daily driving"