pipes on 06 rk

[jazzman713]

im getting ready to put a zippers  hi flow kit on with a tfi tuner. i have been told that the 07 stock pipes are a good pipe? i was thinking of going to a 2 into 1 but if the 07 are ok no need to spend the money?how much more would i get out of a 2 into 1 for 500 to 750 for a 2into1 thanks