"pk gear" vs "pvm gear"
Gear is gear. Any gear can be used for either. It just so happens that when players go into the wilderness, they want to have any advantage they can get, which usually means hitting higher, which translates to vesta, etc. It's easy to do this because you arent taking many hits and the gains make up for the costs (if you dont die). This advantage doesn't matter as much in pvm since you dont have to hit as much. That's why most people will use bandos when killing bosses. They tend to have minions, so you're getting hit often, which costs a lot of money to fix. If you go a long period of time without getting a rare drop, you'll end up losing money through fixing your armor.
I understand what people say when they designate armor pvm vs pvp, but I personally don't agree with those labels.