The scale does not go above 5, mainly because the destruction factor does not compute after the strongest hurricanes on record. Not sure I fully go along with it, but apparently there is no worse destruction past 180, as it is designated catastrophic above a Cat. 4. It seems to me, if the unthinkable 200 mph or above occurs, like an F3 tornado, it can be worse.
I guess past thinking is, when buildings are gone, nothing is worse.