November 27, 2013 10:18 AM EST
I answered your first question in my Wolf guide, it appears to cap at 30.
As to the second, the game has coded values: 'KillMoveRandom' (default: 50%), and 'DecapitationChance' (default: 40%). They only trigger as finishers. Its not a chance to do a one hit kill, but raterh a chance to finish an opponent below a certain health threshold, it essentially replaces the last hit or last couple hits you would have to do. Other things like positioning, enemy type, terrain/obstetrical and just plain chance seem to be factors. Also, if you use the slow time ability suggested in my Wolf build, finishers wont trigger for the duration as the kill cam uses a similar slow time effect. They are supposed to only happen on the last enemy in combat, as they leave you somewhat vulnerable.
The don't do extra damage: they're aesthetic