By the time you are level 81, these stones aren't truly useful. I was talking about being a level 81 char, since I was talking to someone with a level 81 char.
What are you talking about? At level 81 the only things that can possibly hurt you are dragons. By doing this order:
1. Vampire
2. Necromage Perk (Resto tree)
3. Atronach Perk (Alteration tree)
4. Atronach Stone.
You end up with 100% spell absorption. Nothing magic based, (like dragon breath) can hurt you.