Also, why would you need to de-stroke the motor to get it to rev? IIRC, the 22B STi had an 8K RPM redline, just like the other STi cars. You would simply need STi heads or upgraded valvetrain in WRX heads.
I'm sure that you could safely spin an STi motor to 8500 RPM with an aftermarket ECU. Cobb Tuning would be a good place to start asking questions like that.