If auto-attack is implemented, adjusting weapon speed by using stamina cost would seem to be the most efficient way to implement it, as it uses an existing combat sub-system to control the speed, instead of making a new one.

However the case, the stamina costs for each weapon's auto-attack should be varied considerably. Axes should be slower than swords, so their auto-attack stamina cost should be higher than the auto-attack stamina cost for swords.

Has anyone thought about having armor effect the stamina gauge? So that a character wearing lighter armor has his stamina gauge refill faster, while a character in heavier armor has her stamina gauge refill slower. Combined with the above, it could allow for some interesting variety for players to experiment with. A lightly armored Marauder's auto-attacking axe could be as fast (or faster) than a heavily-armored Gladiator's auto-attacking sword.

Just a thought.