YHZ Pilot;
In response to you question on spoiler blowback: There is a speed that if the spoilers/speedbrakes were to be deployed the amount of hydraulic pressure is not great enouth to allow full panel deployment. This point called "blowdown" is not the same for all aircraft and not even the same for all the spoilers/speedbrakes an the same aircraft, as the panels very in size as do the size of the actuators/pistons.