I run an FMF fatty and either a turbinecore sparky (off-road) or the shorty for the track on my 06 CR250 and you will likely need to re-jet anyway. I also run a JD kit on the stock carb and this really helped as the late model CR's stock jetting was pretty sketchy. I agree that a Pro Circuit pipe and silencer would be a great choice if you are looking for a top end oriented powerband. I like the FMF because it smoothed out the low to mid transition on my 250, it all depends on what you are looking for.