I've been looking at different exhaust options for my '12 Ninja 1000 and was wondering how restrictive the factory mufflers actually are compared to aftermarket slip-ons. I actually like the look of the factory ones but would like to get the power of a cat-less header and the weight savings. What do you guys think of using an Akrapovic header with the factory cans? I also wouldn't have to worry about clearance issues with bags in the future. I just don't want to be leaving a significant amount of power on the table if they truly are that restrictive. Thanks for any advice.