I've been wondering the same thing, I've never done the Chilly Hilly and I've only rode in cold weather once or twice. I think I'm going to wear a merino jersey with a Showers Pass rain/wind jacket on the top, then cycling tights with cycling shorts underneath, woolie boolies for socks. Hope that's enough. I did a couple rides in the 30's/40's with the same clothing and felt fine.