Steel legs

At the moment im am pondering weather to get 5 def or not. I pk and seem to b always having the high 8s by rangers hitting on me. So i was wondering wat deff bonus steel legs have…
Plus should i get 5 deff even if i pk
My stats are-
strength-39
attack-31
prayer-17

keep 1 def u want to be able to hit hard and often also alot of f2p pkers are mages and u dont really need def for them