In the power department you're not going to get much...atleast not compared to the $$$ you're going to spend, the factory exhaust is pretty free flowing. Sound...depends on what you like, I'm going for the Bullitt mufflers and mid pipe once it comes out on the market, I like that deep old muscle car sound, If you like the rhaspy loud wanna kill your neighbor sound you can go with SLP loudmouths, tons of choices i'ld go to Mustang meets and listen to different exhaust systems.