Maybe don't change too much from Legendary, just add + and add more gold from 5 to 6 like the picture below.
Legendary/ (pronounce: "Legendary Slash") sounds much cooler.
These might "sound" cooler, but what about adding a BTC symbol instead of anything random.
Legendary BTC or BTC Legendary
While I remain opposed to another rank, I would argue (if there really is a new rank) for a clearly visible difference from Legendary status. Like for example:
Epic
Elite
Veteran