The quests that you should be completing are:
_The Fremennik Trials
_Dragon Slayer
_Monkey Madness
_Nature Spirit
_Holy Grail
_In Search of the Myreque
_Heroes Quest
_Desert Treasure
_Holy Grail
_Swans Song
_Making History
_Mountain Daughter
_Recruitment drive
_Restless Ghost
_Priest in Peril
_Ghosts Ahoy
_Rag and Bone Man
_Rum Deal
_Spirits Of The Elid
_The Great Brain Robbery
From my opinion and experience, i have a zerker pure perfectly made. A zerker pure should be: 75attack, 99strength, 99hitpoints, 45defence, 44prayer, 94mage+, 90ranged+, 4summoning maximum which won't affect your combat.
In your case, you have 80attack which rises alot your combat so thats why you should stay 31prayer, a zerker pure must be level 95 in order to be perfect(96-97-98max).
If you want to pk, the best way to make kills is by having a fury on which makes you have very high combo's.
I hope this helps.