It's going to be louder for sure, you just have to figure out if you don't mind a little more drone and the such. It's really not that bad, but definitely louder than stock.
On the performance front, no one AFAIK has dynoed them but many have said that they definitely feel a difference in the seat of their pants
If you don't have money for headers or will not be getting them for a while I would gut them...I know I will be very soon
