I wasnt too much of a fan having walkers with DTLTs. I have a duel/duel 18" mag and the CIS sound was BAD. After putting Berks on and having a HF cat...it took some of the CIS sound away and also some drone. As for performance...I havent noticed any change. Berks do add a cat but the inside diameter is a little larger at 2.25". I'm also waiting on my new UPREV tune because adding cats leans your AFR out.