Is still don't like that this perk works like additional armor.It's just one more boring DR/DT perk and doesn't feel like "adrenaline rush" at all.I think it should give AP bonus of some kind when you are severely hurt.Then it would be in the hands of player to use the APs wisely.
If you want to make enemies, try to change something.
75% = +1 DT +5% DR50% = +2 DT +10% DR25% = +3 DT +15% DR
That seems very nice, but i agree with Jovanka, so i suggest:-Rename the perk as Die Hard-Make a new Adrenaline Rush perk that increase AP and Melee dmg. like in Lionheart http://fallout.wikia.com/wiki/Adrenaline_Rush