Ok I am not expert but I am pretty sure that on a turbo car removing restrictions in the exhaust track reducing back pressure is a good thing all around, torque and horsepower. The only thing it can harm is waste gate efficiency resulting in boost creep. This is what I believe but I have seen a number of post in the 3rd Gen section saying that removing back pressure makes you loose torque.

 

I have always heard that with any boosted car you want as little back pressure as possible. what you want is exhaust velocity.