A little while back, I was in the market for an aftermarket exhaust, and was willing to drop $300+ on a jardine or supertrapp, but then I got some info from a fella who is an experienced mechanic that actually does race bike setups, and he is a KLR rider. He explained that with alot of the aftermarket exhausts, most of the time you get an actual drop in the power curve, and the increase in power you experience is the coming out of that drop in the power curve. Kawasaki spent a whole lot of money on the R&D of the KLR, and maximizing the power that the engine can put out. Of course, there are mods that help increase throttle response, but $300-$500 or more for a couple of HP's isn't really cost effective. For the money, all you are really getting is eye and ear candy. Do the Jet kit or the 22cent mod, and remove the airbox noise supressor, and spend the rest of your dough on things that can make the bike more comfortable, some nice riding gear, or whatever farkles best suit your riding style. The KLR is what it is. In stock form, it does whatever you need it to do. That being said, if you wanna do the 685cc or 705cc upgrade, that will make the bike a different animal. The money spent on the engine work, then the re-jetting of the carb, and new exhaust you will need after the engine upgrade, could be spent on a nice used dirt bike. That's my 2 cents. Good Luck!!!