okay, heres my thought.
if you enjoy being a pure, stay pure and train as much as you can before you branch off into another breed, i mean the people who have responded to this have some pretty good answers to your problem, but there just saying "yeah go zerk it's much more beneficial.
to start off what stats do you have on your pure atm?
50 attack, very fun to pk on and can make quite alot of money if 90+ str + blitz, or 90+ str with around 80+ ranged. alot of quick ko's come into place with these stats.
60 attack, not that different from 50 attack but reccommended to have 95+ strength as many people have this already at 60 attack. you could use the "dds" and go for massive xp drops and record videos or you could buy a pair of claws and get fast koes again, the fun way of pking and money making way would be 85 range using a magic shortbow - claws which is a nice and easy combination, you should be able to get a ko everytime, unless there ROL faggs.
Berserker, i have a berserker. there quite nice, but don't listen to these other guys saying oh yeah you must have rfd done and you must have turmoil and whatnot, in my oppinon rune gloves are fine, and whilst training your berserker you will want to have high attack and strength, why? because higher attack improves your hit ratio, for example, myself and my friend fought today, he's a berserker with 99 attack i'm a berserker with 80 attack, weere both 93 strength and we were both in torso firecape bereserker ring fury and bereserker helm charged.
our hits would match but he would hit me more often, why? because of his attack.
so what i'm getting at is, dont become a berserk untill you have high strength, decent amount of cash.
stay a pure untill your atleast 94 mage, 90 strength 85 ranged 90 hp 80 attack.
hope this helped you, also don't forget to quest as much as you can before raising defence, it will save time if you think about upgrading