What's the difference between Miss Fortune and Mysterious Stranger?

The Vault describes both perks in shorthand with the following text:

Chance that name will finish off a target in VATS.

Where name is either Miss Fortune or Mysterious Stranger. However, the official perk text for them is slightly different. For Miss Fortune:

Just when your enemies think they have the upper hand, Miss Fortune appears to turn their world upside down. Appearing only in V.A.T.S., she has the ability to snatch defeat from the jaws of victory.

For Mysterious Stranger:

You've gained your own personal guardian angel... armed with a fully loaded .44 Magnum. With this perk, the Mysterious Stranger will appear occasionally in V.A.T.S. mode to lend a hand, with deadly efficiency.

Is there any functional difference other than gender, or is that it?

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1 Answer

Miss Fortune appears randomly when attacking in V.A.T.S, and has a roughly one in three chance to use each of her attacks, they are:

1. A Knockdown against your current target
2. Disarm your target - the weapon will be flung across the room. If your opponent is unarmed, this result will never occur.
3. Cripple a random limb. There is a higher than average chance of this being the torso, and a slightly lower than average chance of this being the head.

By contrast, the Mysterious Stranger will only appear if, at the end of a V.A.T.S. attack, a foe has less than 150 HP to finish them off with a headshot from his .44 Magnum.

The chance of an appearance for either is 10%, though this can be doubled with the Friendly Help perk, acquired when you receive 15 visits from either the Stranger or Miss Fortune.