Easier to research great answers just by typing in "exhaust" under advanced search titles only. You'll be reading for hours. Tanabe Racing Medalion is my choice and reduced weight by 13-lbs over OEM. It also dyno'd 9.2hp above stock (peak) with average gains of 4-5hp across the band. It might look a bit too aggressive for you though, as it's a "love it or leave it" design.

 

You can go for single or dual outlet designs. Mugen, for example, is 'quiet', alittle louder than stock. Very pricey(titanium) ~$1500.00.

If power gains are what you want, single mufflers seem to be the way to go. But most of them seem very loud.

It's all about what your preferences are.....

Do a search on 'exhaust systems' and you will find more info than you might have time to read (or want to read for that matter)

Happy hunting/shopping