You can also ditch the performance pipe and go with a can-type muffler. That's what I ran on my baja 5bss when I had it. I couldn't stand the sharp/loud performance pipe long enough to even finish a tank. I replaced it with the larger 5T can and ran silicone pipe from the can to the rear of the buggy. It was pretty muffled, but still performed ok.
I think I had this one:
http://www.largescalerc.com/15483-hpihighflowexhaustmufflerfor5t5b-1.aspx
The 5B one was thinner/not quite as fat and I had ordered that one to try before the buggy showed up. I'm not sure how universal they are, but might be worth looking at.