You dispell if you have enough "success dice" (that is equal or superior to success dice at castin). so if you cast the 3rd level flcikering fire and score 4 success dice, then your opponent needs at least 4 success dispell dice to nullify it.do i know cast flickering fire at the three warp charge level or the two warp charge level? my hunch would be the two charge level, but I'm sure.
bonus question: are the horrors now able to run in the shooting phase?
Plus, you can run in shooting phase as any psyker can now shoot with his weapon.