On RuneScape, Should i get 99 mage or just cut it at 85?

so basically i started a week ago at 65 mage, now im at 83, my original plan was to get 99 in mage so i can get the cape to look cool and etc. But as i started playing more and Pking and etc with other folks they tell me just to get it to 85, cause 99 is not worth it, and at 85 you can use the tele block spell, which is good for pking in the wilderness. So anyways. What do you think i should do. Basically what im asking is is that is 85 to 99 that big of a hit diffrence? Would i be alot more powerfull with 99 mage over 85? Or do you think it wont even matter. Ive seemed to stop caring about the cape now too. Anyways. What do you guys think. Thanks.