I own a chain shirt IRL. Like I said earlier, I teach a class in how to make the stuff, and having a shirt for people to try on is a draw for the class.
I'd call it Light armor. It doesn't impede ground speed at all (i.e. no Movement penalty). The extra 25 pounds on the upper body might make you a touch top heavy, but other than that it's no an impediment to Dex either. (Naturally I have a 22 IRL, so I know all about that...
In reality, you could forget you were wearing it within 15 minutes. Like I said, 25 lbs, but it feels like 5 once it's on, because the weight distributes so well. And that's 3/4 hardened spring stainless, not the aluminum stuff you see at costume shops.
Now at the end of the day, just walking around in it you'll feel it in your legs. No matter how well it distributes, the weight is still there, so if I were writing the rules I'd apply Armor Check Penalties (a 3.* reference) to any fatigue or exhaustion checks.
As far as Int to Dex: I appreciate the value of a good combat strategy, noting an opponent's style based on how they move and what they favor. That also factors in to your offense as well. Still, I'd be more inclined to tie that in to some sort of skill rather than raw Intelligence.
Or we could call it "leveling up", and see the defense gain not as an AC boost, but as more hit points (presuming that you see hit points as the ability to roll with a punch and minimize damage.) That would also account for the gain in offense.
As far as Dex is concerned, remember that the game simplifies such things. In real life there's manual dexterity, hand-eye coordination and "nimble". I used to be a professional magician and my manual dexterity is ridiculous. Not kidding. At the same time I can't hit a trashcan with a thrown piece of paper, or a hamper with a dirty sock. My hand-eye coordination sucks. I'm also a bit overweight and I have a bad leg, so when it comes to "nimble" I'm definatly not. We could probably subdivide the other stats as well, but we'd be adding complexity to the game, and I don't think the cost/benifit balance is there. We account for things like my manual skill with, well, skill. Specifically Sleight of Hand.
Odd historical note: One of the first iron usng cultures in Europe, and thus one of the first with iron weapons and armor were the Gaels, whome we tend to think of as the Irish and Scots. They discovered and started to work Iron starting in about 385 BC, in an area north of the Black Sea, known as the Blue Mountains. There's a National Geographic article titled "The First Europeans" that charts their travels, and how they ended up on the opposite side of Europe. Good read if you can find it.