training wall has more hps i believe. But with more hps - your hostage will definitely be way off. I think the training dummy is the closest thing to estimating raid trash mobs - inasmuch as they die quickly.
The training wall and the dummy are exactly the same that I recall, in terms of hp. I've killed the wall in 13 seconds before. SoH mobs may go down that fast, but most TSO mobs last at least 25 seconds.