Anyone have any experience with exhaust on the 400ex? A friend has the FMF powercore4 and works well, but i'd like to try something different. How about the WhiteBros new R series? I like the non-disc style, wifes 300ex has the Megamax2 and tired of disc bolts always vibrating loose. At this time I'm not interested in doing the headpipe, just a slip on style spark arrester/silencer that adds power and throttle response.