Re: CleanMPG Reviews the Aerostich Darien Jacket and Pants
You are correct that the Roadcrafter is great for wearing over clothes, suit or otherwise. I don't think it is any less bulky than the Darien, it may be more bulky in fact since it is made out of heavier fabric.
The limiting factor in the Roadcrafter as far as weatherproofness is in the long zippers that the rider uses to zip into the suit. If I understand it correctly, the Darien pants are put on in the conventional way, one leg at a time. It is a comprimise for the sake of convenience in wearing it. I guess I never really think about it now, but that aspect of it makes the suit something that makes riding a motorcycle easier to do, and more safely.