removing the restrictor will give you about 15psi, which is around double the standard boost. Doing this with a standard exhaust is fine, you wont get as much power as you would with a 3 inch system. It will be a big improvement and the car will kick ass. To be safe you should get a new boost guage and monitor the exact boost the car is producing or you might end up with a little ceramic turbo wheel stuck in your cat converter...