The A/T will attempt to fly the speed selected in the MCP. Thus there first has to be human input; hence the question.
For max X w/v calculations your use steady wind + 1/2 gust. The minimum Vfly additive is +5 plus all gust. If the wind is really all X, but gusting I can't believe it will suddenly become all headwind. If it is from the right it might even become a little tail. Adding ALL the gust, with little headwind to reduce ground speed, could cause floating and all the associated consiquences. It is not an exact science, even though people make it out to be so. A modicum and airmanship is always a good idea.