Before I decided to travel from Portland ME to Portland OR I researched whether it made that big a difference due to the wind. After a lot of research it seemed that the direction and the wind probably wouldn't have a major impact on the trip. Let me tell you from personal experience that if anyone tells you this, they have never ridden east to west!!
I'm convinced that we would have shaved 1 to 2 weeks off our 10 week ride if we had gone west to east. It doesn't make that much a difference east of the Mississippi, but once you get into the fields, grasslands, and the deserts of the west, there is no hiding from the consistent west to east headwind. Idaho and Oregon were by far the worst, but South Dakota, Minnesota, and Wisconsin also had their share of head winds.
So take it from one experienced rider, if you need to get across quick, west to east may be the way to go.