Hi,
It does hurt the torque on the 2.5i. I was getting too much back pressure on mine when I replaced the single to a dual exhaust, so my low end torque dropped significantly. The car really struggled to gain speed from 0-30mph off the start. On the high end side the torque is amazing, there's a huge difference. My buddy told me to install a cold air intake which should help a lot and balance it out. I just can't find one that'll fit this car. Oh I forgot to add that I had to take the car back to the shop and they had to make the pipe smaller, essentially choking the exhaust to slow down or reduce some of the back pressure. That did help, but my word Subaru is making it hard to do stuff to this car. Even wheels are a pain in the butt.