It's my understanding that for every 1 armor rating you get 0.12 damage resist, so 80/0.12=666.6 recurring. But when you have 4 armor pieces on you get a hidden +100 armor rating, so the cap you need to meet is 567.
Does that hidden armor rating work with clothing? So if I have robes, shoes, gloves and a circlet do I get that +100 armor rating?
Unfortunately, clothing does not count for the hidden bonus... this is confirmed.

You left out some of the stuff about finishing moves... Namely that the decapitation perks don't cause an insta-kill but only kill if the blow would have killed anyway, and that they (normally--I don't know what happens if you change the decap % variable to 100) only apply to the last man standing.
Thanks for the reminder, Sparrow... I'll add that to the odds and ends section. Hey, at least I remembered to put you in the list of contributors like I promised so very long ago.

Thanks a great deal for putting this together, especially the blocking information. Basically, if I'm reading that right, one single perk point in blocking + a 40% fortify block enchant (which should be doable with base 100 enchanting and perks but no alchemy buffs, correct?) would be enough to max out block with any given shield in the game, or four/five shield wall perks and you don't need a fortify block enchant at all.
You are correct about mixing enchants and Block perks... it is very easy to hit the Blocking cap, as you can see, and for the most part, it is unnecessary to even get the last perk in Shield Wall. We were very surprised to discover this upon testing, as you can imagine that it might have been tougher to get 85% damage mitigation, but... there you go. It is what it is.
Finally, minor point, but another virtue of the Steel Smithing perk is that a lot of "unusual" weapons and armor, like the Blades sword, scimitars, and the Falmer boots, gloves, and "armor" improve using it. The Falmer armor (apart from the helm) also has the same weight and stats as Wolf Armor, so it's worth considering for people who want Wolf Armor's efficiency with a different (and, let's be honest, much skimpier) look. I suspect the set bonus perk won't work with it though due to the helm, but I could be wrong there (I just use it on my followers).
Yeah, I should probably add a blurb or something concerning the Steel perk's versatility... it might take a little creative editing to put it in the correct place, since that post section is so long that it makes the "post edit" function all wonky -- that's why Cheshyr originally separated the sections the way he did. When I reposted the sections to make thread 9, I had to go back and re-format that entire wall of text to change anything in there, and it was quite the pain in the buttocks region.

-Loth