Well, I don't know specifics on weight, but it will be lighter than the stock exhaust.
Gains are supposed to be 15-20 RWHP. But I haven't seen a dyno from anybody here. There is a dyno from japan showing 15 RWHP, but the car cuts of at 120mph. You can go to 5zigen's website and get more info if you can read Japanese. That's all I know. Retail is about 1800+shipping on this, I am selling it for less
5Zigen - ProRacer SP Full Stainless Exhaust