I was looking at this enchantment and I started wondering. If Im at 100 skill does this enchantment matter? Does armour rating depend on skill also? so that more than 100 skill in heavy armour is useful? How much does skill factor into this?
If it improves your armor skill then yes, it should affect your armor class. I'm not sure what it will do if you are at 100. I suggest you save your game, then do the enchantment and see if it makes a difference. If it doesn't reload your save before the enchantment.
I noticed yesterday that my "legendary" improved armor and weapons could suddenly be improved again. It didn't gain any new title besides "legendary", but I was able to improve the stats. My smithing has been at 100 for a while, and the skill hasn't gone beyond 100 (as far as I can see), but I've been doing a lot of smithing since I hit 100 and suddenly I could improve my stuff again (beyond what I thought was the cap at a 100 smithing skill)....
Let us know if you gain anything with that armor enchantment.