I just sold my HKS Carbon TI cat back. With a stock car, I saw no performance gains at all, lost low end torque. Top end was a little better, but for the money I paid, it was very small gain. I am not goin with a full turbo back system due to warranty reasons, but would like to install a rear section exhaust. I am goin for either the Turbo XS original, the new turbo xs Ti, or the buschur racing 2.5 rear section. Does anyone have any ideas on which is best? Please give your opinion? No 3 inch systems wanted.