on a local dyno a stock subie will do 170-175 whp. (its about 25% loss to the wheels since 227 is the stock rated hp) With a freeflowing exhaust and engine management I would put you at about 215-220 whp. That would be with about 25% drivetrain loss 270 hp.
Those three mods are worth maybe 50 HP. Just imo... your mileage may vary.
EDIT: If you are going to go further and buy injectors / turbo / intercooler I'd buy a UTEC. If not, I'd get an accessport.