As mentioned in the Detailed Instructions document, there's no such thing as bad weather only the wrong clothing That's why many LD riders wear waterproof textile gear, so you can just zip things up when it gets wet/cold instead of keep having to stop and put on/take off leggings and/or over suits.
Having said that during a couple of the early RBLR1000's we had horrendous driving rain for many hours heading north so an oversuit and even overboots came in handy over the top of my already gore-tex gear.
I was going with the logic that my textiles are much more comfortable on big days without the waterproof liners in but this does mean anything more than a 30 min shower is a rain suit stop!