EXC is a plated bike and I am not positive in Australia, but in the US, they get smog devices and they are mapped accordingly which does not let them breathe. Plus the gearing is a little tall as well for street use so you will loose the throttle snap in the midrange. Adding a slip on will help, but you will most likely need to remap the bike. Most people load the XCW map in the bike to give it a more broader power range. I would also look at the gearing on the bike. re-gearing will make a Huge difference in the power delivery.