Was There ever a EF6 Tornado Rank?

Sort of. On the original Fujita scale theoretical categories F6 to F12 were plotted, but they are never used, as ratings are based on damaged, and an F5 tornado leaves nothing left to destroy. Since it was never used, the Enhanced Fujita (EF) scale did away with it completely, giving any tornado with estimated winds over 200 mph a rating of EF5.