^^ words of a pro there. (although not sure i agree about what the creator should be able pass the track in, cos that really depends on how good at the game they are. its possible to create very difficult but effective tracks without having uber skills on the game imo)
ignoring ninja difficulty (which should be massively harder than extreme in my opinion) to gauge extreme difficulty i would recommend using the in-game extremes. create your track whilst keeping the difficulty at least around brown boxes level and make sure its not much harder than inferno or diabolic. hope that helps a bit
