Borla claims more hp but no numbers. A member here dynoed an FRPP version and put down 392 whp, another member with a borla sport version put down 386 whp. No stock runs before the application though.
The results varies,but i m sure it flows better than the stock due to their welding and elbow teqniques. A catback should be good for max 5 hp in my opinion, and better area under the curve. You are also loosing 30 lbs. Even a loaded car can weight below 3800 lbs just with the Borla catback swap.
Axlebacks might not even give you any gains due to stock suitcase and piping. They are mostly for sound.