I've got a similar question about freezing my own *** off, but on a slightly different route. My plan is to cross the US on Adventure Cycling's TransAmerica Trail. This route is farther south, so I'm hoping for a bit more warmth.
The sooner in the season I could get started the better. I figure going east to west will let me start sooner, as the eastern end is farther south and it would postpone the rockies for several weeks.
Anyone done this trip from east to west? How early in the year is it reasonable to get going? For personal timing reasons, earlier is better, but not so early that I'd freeze or suffer endless rain.