Well, had my first run on a tank alt where I survived by the grace of what little Tenacity I couldn't shed. At one point, with no CDs left to pop without screwing me over later I ended up at 28 HP even after popping an HP potion (left on my auxiliary bar from HoH). Tenacity mitigation at the time... .9%. A few other blows dropped me to <1600 HP, so that was probably more than just the Tenacity difference, but still...

I don't think my subconscious will be dismissing mitigation stats from here out.