Agree with everything everyone has said about addy gear. It is much better to dedicate it to edged weapons than armor. Steel, bronze and even iron are pretty much as effective, or ineffective, due to lucky shots generally being what takes your soldiers down. And much easier to acquire.
However, a 1-tile-wide entryway to your fort is highly effective, I've found. I have the "normal" entrance - wide enough for caravans to bring their wagons. In case of invaders, I wall it off with a bridge and open the "Guest Entrance." It's a twisty (which limits the distance enemy archers can fire) 1-tile wide tunnel that opens into the barracks.
During one recent siege of about 60 gobbos and trolls, I stationed my military about halfway down the tunnel. One of my swordsdwarf recruits was at the head of the line when the gobbos came around the corner. He charged and proceeded to slice his way through the first 8 or 10 without injury, gaining a title and a bit of skill in the process. The inability of the gobbos to dodge effectively - they can only dodge forward or backward - and the fact that he had steel armor and a steel sword let him walk through like a moving food processor. The gobbos that dodged behind him, or when he dodged backwards or around the next corner just exposed the next soldier in line.
It's very much a "300" strategy where you prevent the enemy from surrounding or getting behind you by forcing them through a chokepoint. That way, a few effective soldiers can beat a much larger force since you are forcing them to fight one-on-one. And they don't need addy gear to do it.