Never heard of a legal limit for wind speed in absolute terms. The only planning limit that I´m familiar with is the cross wind COMPONENT. So if the mean wind is say 60kts perfectly aligned with the RWY centreline, you can plan it that way, since the COMPONENT is 0.
Gusts only have to be considered for ETOPS alternates as far as I remember, for everything else you just have to consider the mean wind.
I´m not 100% sure right now, but I think in the example given by bookworm, you can also stick to the mean wind.
As with the other minima, you can depart when the destination doesn´t fulfill the minima as long as you plan it closed (-> 2 alternates).