I'm new to the forums but really enjoying reading all the thought and ideas that people have on the subject some of which I think are really interesting and some of which I honestly think would be a detriment but that is the reality of game design you aren't going to make everyone happy. As for myself I think gameplay and enjoyment should take presidence over any other mechanic or attempt to be realistic. I know many people have suggested that wearing Heavy Armor should confer a movement penalty which would be more realistic and make a decision to wear it more tricky however I think that is a bit of a tricky question as movement has a large impact on the game as a whole. This is also going to be effected by other systems in the game for example what is going to be the main mode of travel if it is going to be walking and if you say you walk 10% slower in Heavy Armor then what is probably going to happen is that people who want to use Heavy Armor either have to just put up with being slow (which isn't fun and could get really annoying) or keep another set of armor they have to change into in order to move at a normal rate (which again isn't fun as having to change armor just to get around annoyances like that is more likely to make me annoyed with the game then make me want to keep playing). However if the main mode of travel is going to be via horseback (as an example) and type of armor doesn't effect your movement speed while mounted on a horse then it is alot less of an issue. Another idea might be to have the movement penalities only apply when you are in combat which solves the general movement problem at a loss for realism which may annoy other people.
In regards to tiers and upgrades for armor I would be much more in favor of something like Iron -> Steel -> Mithril -> Ebony -> Crystal (or something similar I would just using random heavy armor types) then have Plate Armor -> Plate Armor +1 -> Plate Armor +2
In regards to descriptors such as a Fine Iron Helm or a Superior Iron Helm that really depends on how you want to treat them. I like the way Skyrim handled it where the base materials were the tiers (Iron, Steel, etc) and then the prefixes denoted levels of improvement upon that tier so that a Steel Helm would be better then an Iron Helm but a Superior Iron Helm (with Superior indicating 2 levels of refinement) might be better then a Steel Helm.
I like the idea of having a wide range of armors available but each with different benefits and drawbacks some of which might not have anything to do directly with damage avoidance or mitigation. It is definitely going to be very tough to get a system that feels and works well that a majority of people like
