Well, you shouldn't take the Threat meter too seriously...
Rogues can reset their threat, Assassin's Grimtooth has double threat because of the self heal, Potting also influences it, as well as any sort of heal, self-heal or those with an extra Threat modifier boost like all the Tank classes.
Anyway, if you want to DPS the most as possible with your Assassin, you should max both <Shadow Strike> and <Shadow Explosion>, and also add some points to <Grimtooth> (lvl 6 is just as good as <Double Attack> DPS wise) and if you can afford it, max out <Poison Weapon>, <Shadow Fiend> and of course <Shadow Form>.
With those as your base, your DPS should be as high as possible...
The rotation is simple, only use Shadow Strike when Shadow Explosion is ready to use and you lack Combo Points (so the points arent wasted) for a chance to get a 30% extra damage.
Here is my rotation:
Shadow Strike -> Double Attack x 1-2 -> Shadow Explosion -> Grimtooth -> Double Attack 1-2 -> Deadly Blow -> repeat.
The only reason I use <Deadly Blow> is to deplet the acumulated Combo Points to take adventage of the 3 generated by Shadow Strike. You can just skip it and ignore them, then go ahead to restart the rotation.
Edited by Leinzan, 03 January 2014 - 07:55 AM.