This was the first I ever heard of the berserker necklace effect, so I decided to do some research on it. All information is from either the Knowledge Base or the max hit calc. This is using cheap armor that most people should be able to afford, so it's not the best possible stats. Obby Sword, Berserker Necklace: +39 stab +70 slash +72 strength +185 stab +205 slash +184 crush +182 range 26 max Obby Mace, Berserker Necklace: +83 crush +89 strength +183 stab +202 slash +184 crush +182 range 28 max Obby Dagger, Berserker Necklace: +70 stab +60 slash +82 strength +183 stab +202 slash +184 crush +182 range 30 max Abyssal Whip, Amulet of Glory: +115 slash +114 strength +203 stab +222 slash +204 crush +202 range 28 max Armor: Helm of Neitiznot (Berserker Helm may be preferred because of higher def bonuses), Fire Cape, Fighter Torso, Rune Legs, Rune Defender, Dragon Boots, Barrow Gloves. Better armor would make the obby weapons more useful because the -20 defence would become less significant. The max hits are with 84 strength, no pot, no pray, according to the max hit calc here. I was kind of confused, but apparently the dagger is better than the sword. You might say that the 115 slash of the whip means it should be used everywhere, but remember that a Berserker Necklace makes all obby weapons hit 1/5 harder. This means that a 20 would turn into a 24, making obby weapons hit harder, more often. According to this data, you would use whip if a monster is weak against slash, mace if weak against crush, and dagger if weak against stab.