First, you should really consider getting basic IOs instead of SOs, as if you invest in level 30 IOs your're slightly better off enhancement percentage-wise and save a ton of influence by thr time 50 rolls around from not needing to constantly upgrade the SOs.
Secondly, I also reccomend DM/SR if you're not doing set bonuses, as you can soft cap positional defenses and get the DDR to +95% to resist debuffs without set bonuses, unlike /Shields.
Quickness, along with Hasten + attack slotting helps you achieve a good attack chain, since you're not getting recharge from set bonuses. I haven't loaded Pines up with this to see what you'd be able to squeeze out without sets, but if you can get 235% recharge (with Hasten) in Midnight's Grasp, you can run the optimal ST attack chain of MG>Smite>SL>Smite.
Finally, DM gives you a self-heal in your attack chain, end management, and a to hit and damage buff, all of which /SR lacks.
Finally, and this is big, if you're doing basic IOs (or SOs), you won't be using -res procs, so DM's damage type really means a alot for effectiveness.