Hmm, in my experience last night (watching stalkers) you can't really one-shot anyone. What you can do, however, is wait until they're distracted / damaged and then you can knock anything up to about 75% of their health in one shot (or 30-40% of a tank) and leave them cursing you and crying for nerfs
Dreamreaver : Level 18 Necromancy / Dark Miasma Mastermind