I would suggest for realisticish damage you try using the battletech rules with modification. roll a die to see what part you hit then just start thinking about the size and shape of the weapon (I sincerly doubt a quarterstaff would be able to knock off a limb but it might break it. By the same token an Axe wouldn't even come close to not cutting somthing unless the person is using the flat of his blade).
Also one would try to put in modifiers based on the size of the weapon vs the size of the opponent (don't think a maul the size of the rock of gibralter will hit a mouse but if aimed at an army you can kiss that army goodbye).
SO... one should try to make their rules fit the situation but have at least some basline to work off of.