The Rs Max Pure, since it has 99 in all of the melee combat skills, you will be able to wear pritty much anything, except the quest items you have not obtained. If you have obtained the quest items, you will have yourself a very good account to own many players.
Since you are already have the highest levels in all of the combat skills, you will not need to train, unless you love to train and want to max out your experience in a skill or if you are training magic or range. I will explain training magic and range in later articles pertaining to their pures, so I will continue with armor for pking.
As an Rs Max Pure, you should have a good amount of money from training at bandits or at other random monsters for another skill, like slayer, or from having fun and pking. In that case, you should be able to wear a good amount of armor, and be able to lose it, without it taking large chunk out of your money supply. The armor for an Rs Max Pure is an Abyssal Whip, dds, barrows gloves, rune defender, amulet of glory, and dragon boots with full rune.
If you are very talented and have money to waste, you can wear barrows armor for better protection. If you are poorer and want to pk, wear the same thing stuff as a Max Barrows pure or the regular Barrows Pure. If you are a Max Barrows Pure and do not have enough money for armor, I would suggest taking a look at a money making guide to help you out in other parts of the game, rather than concentrating on pking.