I use OSM a lot also. Most of the open spaces i hike in were once ranches and homesteads (Los Angeles). One of the things I like to do is find old trails and ranch roads that are no longer on the maps and haven't been used in decades; or the locations of old homes and other points of interest you can only see in satellite photos or old aerials. If its a historical aerial I would calibrate it using google earth and import the kmz into the garmin. And of course, I would convert historical paper and digitial maps to kmz also. With some of the tools I have been playing with I have more options on the type of map to use. There is not much info out there on just how a jnx file differs from a kmz file in terms of performance -- even just from a theoretical standpoint.