I've got lifetime map (road map) upgrades for my Zumo 660 and indeed most of my riding is on roads. But with my new F800GS I'm venturing off pavement and would like to know where I am... I also have an Oregon 550 with a Garmin micro-SD card of North American Topographic map data. My Zumo 660 accepts that card, and when I check the map info, it's selected (checkmark) as is the road map, but going off-road I don't think any of the topo stuff is showing. Can this be done? Or should I just mount the Oregon 550 on the bike and use BOTH of my GPS units? Would that be a better option? Thanks!