Both, you dont have to make more noise to make better noise... change out the slip ons and get rid of the cat. The sound will improve, deeper and more powerful. straight pipes often sound tinny and pop or gurgle on decel, plus they just **** off a lot of riders, drivers and people in general
They do sound bad with the baffles removed and I'm sure performance suffers also. If you are looking for a bit more sound then I know on my 11 RKC by removing the CAT gave it a bit more rumble. May be a cheap alternative and give you the sound you are looking for. I'm happy with it.
To the OP. I found some vids on youtube from somebody that did a de-baffle on a 2013 street glide. Should be exactly the same. 4 or 5 videos I believe. He seemed pretty happy with the results. Here's a link to the first vid. Good luck!