It is hard to asses the dps aspect of Shock Charge. DoT damage is small but incremental, and can make a big long term difference. The add-on skills give utility, but my real interest is a basic damage comparison, to decide which skill is better (Shock Charge or Rapid Shot).
Going by TORHead's values, Shock Charge does 2581 over 18 seconds. Speed Shot does 725-1109 per activation. In a 90 second time frame, Rapid Shot would provide 2 extra Speed Shots, but Shock Charge would have 5 activations. Eyeballing the math, 5 x Shock Charge > 2 x Speed Shot.
So individual ticks of Shock Charge are much smaller numbers, but overall it appears to give more punch. Considering crits, even if every Speed Shot did *double* the damage, simply applying Shock Charge on each cooldown still beats it out.
Of course, this assumes that TORheads values are accurate, or at least represent the proportion of damage between these abilities correctly for the same gear.