I know I'm going to sound like a broken record but....how fast is each secondary attack animation? Not the attack speed that the unit is set for, I mean the actual animation itself. All these bodyguards can have the same attack speed, which basically just sets the cool-down between attack animation runs. If the length of the animation of the attack differs by any great amount, however, then it will still be a tangible and noticeable difference.
Also, when the tests were being run by CuteWolf did the defending human just sit and allow the charge to hit home or did they counter-charge? I've found that the AI goes about 50-50 as to whether they counter-charge my attack or not in battles. If you're just sitting there there's always thepossibility that the attacker can win by getting those few extra men free to gang up on enemies.