Playing around with stuff, I'm getting better results with stacking accuracy to 141% seeing as shadow strike has a 50% armour ignore from talents and you get a passive 9% from the kinetic tree. This means Shadow strike with the buff up has 100% armour penetration and does a lot more damage to everyone, my highest shadow strike critical so far has been 4.6k
After accuracy I go with critical but not getting to much, still using the critical/surge relic from the pvp vendors though.