When wind speeds get to 40 MPH to 55 MPH then the wind can make it difficult to keep control of your vehicle.
So if you drive in those wind speeds you need to really pay attention to the road and keep your hands firmly on the steering wheel and if the wind gets too bad and starts pushing your vehicle around you may need to pull over and wait it out.
I find that sometimes when the wind starts to get to 55 MPH my car starts being pushed into the next lane so I really have to watch my driving.
I would personally say anything 55 MPH and above you should really not drive your vehicle unless absolutely needed otherwise it can cause you to lose control of your vehicle.
It can cause your vehicle to go into other lands or even push you off the road and even possibly push your vehicle into oncoming traffic especially if you're driving a high profile vehicle.