If you're going to stay at 60 for a while and pvp for the set, you should work on the masters that will help you most. Evade an high damage are most important.
I never played assassin but would do assassin's masters in following order:
Physical Critical Hit Chance
Decreases MP cost
The decrease of malice you won't need at all in pvp. Pvp isn't about malice.
Maybe you can find some more helpfull information in this section of the forum