Unstoppable: Heavy armor skill tree, active skill.
I suggest Unstoppable make the user truly 'unstoppable' for the entire 8-10 seconds.
Its a 400+ point stamina suck that lasts 8-10 seconds and the user is not truly unstoppable, just mostly so. (Talons)
The duration is short enough and the cost high enough I believe that being truly 'unstoppable' would be justified.