In Alberta on highway 2 and 22 the wind can really blow. 80-120+ km/h is not unusual. I have heard that there have been times when it can reach 180+ km/h. I have seen 18 wheelers on their sides in bunches up these roads.
If you keep going 100km/h (60 mph) and the wind is really blowing it takes less wind to blow you over, depending on the direction of the wind. Head wind is bad for gas milage but not troublesome otherwise, tail wind can increase milage but push you around a bit and a cross wind can blow you over. The effect of driving at speed plus the wind compounds the forces that can blow you over, if you slow down you reduce this force. It’s all physics, (F=M*A) a moving vehicle is accelerating and increase the forcing acting on it. A stopped vehicle would take a significant wind to blow over because the force is reduced.
I don’t know the exact speeds but if you ever feel the unit get wiggly, slow down!