Go back to stock or Trapps and you'll instantly gain about 15hp as well. Cobras totally kill power.
My vote would be to pick up a set of supertrapps...they're widely available, are a snap to install, and sound great. I believe Sean sells them, or I know Dennis Kirk stocks them as well. They're also far lighter than the stock muffler.
Considering the cheapest stock mufflers are going for ~$150 on ebay(all the way up to the
crack smokers asking $900+) you might as well ante up a bit and get the lighter, cooler trapps. I think I got like $120 for my stock muffler a couple years ago.