You might also want to get hold of a copy of the US 24K topo maps for your part of the US (they are not key protected like the street maps are) and load those on both your computer and your GPS.
Where might one get that map? I'm being lazy here as I'm at work, but is that available on the Garmin site? After picking up a DR650 I'm looking at my 550 doing both street and off road use.
I used to have a DL1000 and took it off pavement frequently. Tracks created by others and generally available on the web such as the Backroad Discovery routes are available. The problem with the 550 is it will not import the track accurately. When the 550 imports the track it creates a route based on the internal map.
Heaven help you if the track includes road or trails not included in the map in your GPS. The stupid thing would not accurately import a track I laid down.
Let's say a 1 mile section of road is missing in the internal map. The GPS will create a route going back and forth to the ends of the road in the internal map. Imagine a circle that is 2 degrees from being complete say 358 degrees. The GPS will take you from 1 to 358 degrees because it does not know the way from 358 to 360 degrees.
The Zumo 550 is not a good offroad GPS. I believe the Garmin Montana might be the way to go. The AV rider forum might be a good place to start research.
Over the years I did see a big improvement in the maps. More gravel road were included making the 550 a bit more useful to follow gravel roads but if the road is not in the map you will need some good paper maps and local knowledge.
I sold my Vstrom and only have the FJR so the 550 is fine for my current activity. If I go dually again the 550 will not be with me.