i have an ista breeze 2kw wind turbine and never has the dump load I have done anything to prevent it from over speeding.
even if I bridge all three wires (the largest dump load possible), it still spins flat out in 30-40 mph winds.
its also got a brake function on its controller. which doesn't stop it in 30-40 mph winds either.
so I would recommend some way of mechanically turning the blades out of the wind or having a mechanical brake on the rotor.
A dump load will not help it, also not once has the dump load been activated due to the batteries being full, maybe if i went on holiday for a few weeks and turned everything off this could possible get close to happening.
even though the wind turbine i have is rated at 2kw, even in 40mph winds where the thing is spinning wildly fast, often mind boggingly fast at times, i have not seen over 1100w output with any load on it.