I personally do not remember the date of this, or the combat level that I was at the time, but I DO remember what I used.
Here is a list of all of the PKing Gear that I will ALWAYS PK with.
Dharoks Helm
Dharoks Platebody
Dharoks Platelegs
Dharoks Greataxe
Dragon Dagger Poisoned (I only use this about 25% of the time I'm PKing. I keep it in my inventory and use the special attack when my opponent is low health.)
Amulet of Fury -OR- Amulet of Strength
Dragon Boots
Dragonfire Shield
Warrior Ring
Barrows Gloves
Fire Cape -OR- Strength/Hitpoints SkillCapes
~I also ALWAYS have 3-5mil in my Inventory at ALL times, so that I can buy Food from the Experienced PK Shop.
So, the longest streak that I have ever been on, in all truth, is about 12-14 kills. I will only ask players to fight me if they are within a 20 level radius of me. BUT, if a player asks ME to fight, I will accept no matter their level.
Note: All of my kills were during one on one fights, and my streak was ended when my opponent hit a lucky 73 hit with his Full Dharoks.