So I have a theory regarding the large discrepancies in the girth of the “Sword of Rage” in its various depictions in the artwork.
After careful review and minutes of consideration I believe that the Sword of Rage (tm) is in actuality a metaphor for the Black Knight's "psychic member"!
Like most men, he derives his amazing confidence and power from his own mind's eye view of the enormity of his phallic being at any point in time.
Note in the following two pics the sword is roughly the same size, though it does seem to have thickened a little (not to mention electrified) in the second one.
Just a regular guy with a pretty average sized sword in his hand...
Starting to feel a little uppity are we?
Is the shaft a little thicker...
However, in the Premium cabinet art the Sword of Fury (tm) it has become engorged with power and the Black Knight can barely wrap his fingers around it! He must be well neigh invincible at this point!!
This idea has vastly improved my overall view of the game - I mean who wouldn't want to power up and then wield a giant throbbing Sword of Rage against their enemies!