I've used the stock, the Pro Pipe, and the D&D. While the D&D is the loudest, it returned the best performance. Carb has been rejetted, and the airbox has been modified to flow more air. Was able to hit 94mph. Running the ProPipe now, a little less bark, a little less power, but was not rejetted to match yet. Next will be a modified stock muffler, just don't have the time right now.