I know Mike Marshall rides his Duc in all sorts of conditions. Maybe he'll chime in with gear that he uses. I think he was in full leather suit when we did Angeles Crest but it was summer.
I love my Rev'it gear. It has cinches on the arms and body so that you can tighten up the fit with the liners out and limit flapping. Then when you add the wind/water layer and/or the insulation layer (you can mix and match those) you can "let out" the jacket. This guy is a *great* source for rev'it:
www.beachmoto.com