To my knowledge, and feel free to correct me;
To do max damage Deathstrike you need GM Tracking.
Track your victim for [?] tiles and perform DS on them.
Your following DSs though will only reach 40, to do max damage again you will need to repeat the Tracking procedure.
For that matter I am almost certain you need 100 Hiding, 120 Ninja and 120 Stealth, not just 100 Stealth for the max damage without the Tracking procedure.
Even if I am wrong about having Stealth 120 instead of only 100 it's still a messed up template.