I went back and forth on the 600k. Chance of precipitation started at 60/40 (Sat/Sun), and then went down to 30/10.

I originally told myself I wasn't going to do it if it rained, because I didn't really have anything invested in it, and didn't want to be miserable. Then I resigned myself to the fact I wouldprobably do it, and since I was bringing along the kitchen sink anyway, I brought rain pants/booties. Boy was I glad I did! We had a soild hour or two of some of the heaviest rain I have ever ridden in. And then it stopped, and I had something like 200 miles more to ride, and you know what? I dried out.

It may be miserable for some of it, but be prepared (jacket, pants, whatever) and just take a shot at it! If you do, and it does rain, and you stick it out, this will be one of your best "mental toughness" rides ever!