Impreza 2.5rs 2005 Turbo

i was wondering what is the most reliable whp/wtq i can get on a stock engine components and descent turbo setup and tune ?

what will be the next thing that will be the weak point if going a little higher ?

im also looking into some recommended/similar build

i also might go with another block that ill build with forged internals to eventually go for around 400whp in the long run when all the parts are collected

THX