I have a Garmin GPSMAP 60C that I have used on brevets and BMB. It works great and has kept me from "Bonus Miles" on more than a few occasions. Most of the bike mounts for it suck. I finally ended up with a marine mount that fits my stem with a u bolt. Now it's solid as a rock. See Rienhart Geislers site
www.bike4one.com for more information on this model and GPS use in general.