The Berserkers Ring http://www.thehiddenforest.org/webtools/items.php?id=12424, aside from being morphologically problematic (Berserker's Ring, or even Berserkers' Ring would be more coherent), has an effect, Power of Fear http://www.thehiddenforest.org/webtools/spells.php?id=8697, which does not stack with either of the Berserker donator weapon effects: Berserker Power http://www.thehiddenforest.org/webtools/spells.php?id=8596 or Sullon's Frenzy http://www.thehiddenforest.org/webtools/spells.php?id=9691. It'd be a nice little addition to my arsenal of effects if it did stack, slighty softening the sting of the Sullon's Frenzy cool-down.
Also, would it be so bad to decrease the cool-down for the Berserkers Ring itself? 10 minutes? It would be a fine thing at 5 minutes, a thing of beauty even. Consider rendering the ring even more fit for berserkers by removing the cool-down altogether and increasing, or implementing, the effect's intended AC hit.