weight savings about 50 lbs. gains minimal sound awesome!! takes about 1,5 hrs at any competent muffler shop. i would also recommend considering the secondary cat delete. another 20 lbs saved and imo the perfect sound with the amg muffler!
as for hp gains i didnt dyno so cant speak to that. didnt really feel any diff. but sounds SOOOOO much better!
another thing to consider is using a dual inlet /dual outlet muffler and getting a true dual setup. you only need about 3 feet of tubes to get it done.