I had eight straight days of rain and snow in the North Cascades and Rockies in June last year on my Northern Tier ride. I followed many of the tips outlined above, mainly smart layer management. I kept a gallon ziplock bag on top of my pack to store a dry jersey for the descents. I could get it out at the summits without getting everything else wet. My strategy was to forget about staying dry, but to stay warm while wet. It worked well enough to keep me going. I also kept plastic bread bags handy for my feet, over my socks and under my shoes, for the really cold days. Keeping sleeping insulation dry is also critical. I store all that in a trash compactor bag inside my almost waterproof pannier pack.

As far as stopping to rest, I don't do it in rain, except every couple of hours if I can find some kind of shelter. I keep a steady pace that I can sustain for hours. On hiking trips in similar conditions, I'll pitch my tent for a break, but I haven't had to to that on the bike. There's usually at least some kind of park pavilion if not a cafe. At one of the high passes in Washington State, I met some RVers who invited me in out of the snow for a hot drink and a warm place to change into my descent clothes. That was nice.