Ive just bought an itr, it has full mugen twin loop system(stock cat) with mugen manifold, Ive only driven 3 dc2s, 1 stock, 1 with dc sports header (stock cat) and custom made s/s cat back and my own and i have to say the mugen system just sounds beautiful, not loud just throaty and deep, I cant really comment on power differances as i only drove other two cars briefly, But as ive said my mugen definitely sounds best...

Ive read reviews bout mine and its all very good,