Getting a header/dp w/o cat makes the car extremely loud, but do not get rid of resonator. Having no cat with the dp will give it a deep tone when you get on it as long as your resonator is there, but a high flow cat will have better sound quality. I had all my work custom done and it was by far...
No need to go over 2.5", in fact. I just used stock piping b/c it is 2.5" and replaced resonator with a glass pack and muffler with a borla. Same damn thing as an exhaust and only like $150