I doubt that a stock WRX is 255tq to the wheels. Maybe after a tune + 3" exhaust. That being said, a dyno is primarily a tuning tool, and some dynos can read up to 10% difference.
You'll be reading a good portion about the gearboxes classically, WRX gearboxes have been, well, crap. Not much data on gearbox failures on 08+ WRXs, so that has to be a good sign.
EDIT: you mentioned coming from a 2001 mazdaspeed3. Typo? The speed3 wasn't produced until 2007, not even the Mazda3 was available until 2004.