Does not double stack Does provide unstoppable. Considerably more durable with it than without it No noticeable difference between perk unstoppable and eternal warrior unstoppable It provides bonus damage resistance when using fist of havoc, if you received any damage before activating, you are that much more likely to die before connecting. I like using headstrong and shockwave, so I can use my panic sooner and it goes farther. -[i]An eternal warrior preferred user [/i] P.S. without unstoppable, I've lost many chances at breaker+ medals. Unstoppable is extremely important, but I don't feel like a striker without shoulder charge. Eternal warrior was my ugly answer.