Never found threat to be an issue at all, pretty impossible to get aggro off of a taunting tank. If you've pulled aggro then it's because you've backstabbed something that the tank has 0 threat on in which case Reduced Threat wont help you, armour rating will.
While I'm not 100% but isn't the dusk ring from the dalish elf forest section ? In the first forest area (can't spell name) behind the old oak tree there is a little camp. If you that lil sidequest / event / whatever, either the mob drops it or its out of the chest. I think thats the same ring your talking about but I could be wrong.
I used executioners helm because it looked totally kickass and it had +25 stam (i put 0 points into will ); unfortunately its been more than a week since ive played, but im sure one could google it or find it in that dao wiki.