I'd say one good bleeding or bone breaking impact would be sufficient. There are legends of people who kept fighting with limbs torn apart (even after getting beheaded) or wounds bleeding all over them, but needless to say those are just legends.
Not as legendary as it would seem, I cant find it now, but there was a video of an historical arms expert that explained how the sword duels with one stab/slash endings were unrealistic. Adrenaline is a hell of a drug and he compared this to swordfighting techniques in medieval fencing books. The "finishing" moves you typically see there are not wide arm overhand chops or lunging swings because that makes you vournable to retaliation from the "dead" enemy you chopped up.
They are more conservative with defensive halfswording options and stances because even when you, for instance, put a blade trough someones gut they are still perfectly capable of gripping their weapon and counterattacking. Thus the only true "one hit kill" as described in the video, in the OPs instance last option, would be decapitating the head or severe bodily trauma. Then again, you dont need to "one hit" someone, incapacitating them then halfswording or with a dagger slipping trough the seems of late medieval plate would do the job. That or blunt trauma. So i would probably go for option 3 and 4
Poll