I installed a basani catted x-pipe on my 05gt and I am pretty impressed. I had the slp kit on at the time and it was way to loud after I put the x-pipe on and it sounded like an overgrown ricer! I put the factory mufflers back on for now and it sounds much better. I dont have any dynos numbers but it feels like it pulls a little better and I do have traction problems now that I didnt have before I started modding so it must have done a little bit.