The current scale is quite weird since most Tornadoes are scaled on how much damage they did rather then speed, size and other stuff. For example an Ef5 tornado could happen in a field or a sight where bearly anyone resides and people will most likely classify it as an Ef3 or below.
But an Ef2 could damage an area with low infrustructure and many mobile homes and it could be considered in Ef4. Anyways here are my thoughts on potential Ef6 tornadoes.
-Tri state Tornado
-Bridge Creek Moore Tornado
-Daulatpur-Saturia Tornado
-Joplin Tornado
-Hackleburg Tornado
-1990 Goessel KS Tornado ( One of the fastest tornadoes in recorded history).
