So your cap for deathstrike is 60 if you have everything and tracked them for enough steps. Then you lose half if you have a bow giving you 30 damage. Again this is assuming you have 100 tracking and also tracked them long enough.
You cannot stack specials and spells at the same time. Therefore you cannot "cast" deathstrike and mortal on top of it. There would need to be two seperate contacts. Better to just go with a concussion blow. It's a LOT cheaper in terms of mana cost. If you're human and have max LMC, you can get a conc down to about 8 mana for the first try. Deathstrike is gonna cost you 30 (-40 LMC) which is actually double the cost of conc blow.
Bottom line if you wanna do deathstrike, stick with melee weaps. You can open with a death strike then disarm. That WILL make em move.