Glenn,

It sounds like you are a touring cyclist. If you are not already, I would recommend you sign up for the Bike Touring email list (Phred). There is so much bike touring knowledge there it will make your head spin.

You can sign up here: Touring List

Not that the gang here doesn't know their stuff, but bike touring is a little different from backpacking and hiking.

FYI I prefer synthetic bags as well, mainly because of down's issues with moisture. Using arm and leg warmers allows for a lot of flexibility both on and off the bike, and they roll up very small.

Good luck!

Greg
(fellow tourist)