C) Plate, to me, is primarily for avoiding getting easily killed by ranged fire and teamwork damage.
I remember when I bought low end plate, and there was this clusterfuck where we were charging in nord town, and... two throwing thingies, dead. Just like in mail. Generally it was 2-3 throwing BS and I'm dead. Speed at least lets you close to throwers faster, so plate is more of a hinderance there. It only protects somewhat from archery.
I also took it to duel a bit... I was a polearmer that retirement. So anyway... once it took two slashes from a danish greatsword to kill me. Wat? Then I tried with mail armour to see the difference and although the damage received was somewhat higher, it was much easier and much more effective to fight with.
Basically, waste of gold, get mail.
Also, this Goretooth you speak of was on EU a few times where he got killed just like any other tincan, bah.