I to have been fighting this issue. Have 60CSX and just figured out it will hold only a max of 20 tracks, this seems to be the case regardless of the track data. I wish to do something similar to what you have looked to do. My conclusions:
Save numerous files with up to 20 tracks tracks each, say for a given area. Each file would in turn need to be loaded back into GPS when you need it. These are individual tracks residing in a saved file. use SAVE AS feature to do this. "Tracks cannot be saved to SD card. None of this is clear or even stated in my manual.
The other option I'm working on is using track logs. Example, ride my ATV over a given area (if you go over the same ground more than once turn GPS off or track log doubles) while recording the route on the gps as I move. This data becomes the daily log (amended each time you turn GPS on and off) and can be saved to the SD card if you wish. (on 60csx at least) These logs can be downloaded to mapsource, altered, renamed, saved as different file types. There seems to be no limit as to the number of logs that my unit will hold, limited only by the space available on the SD card. Logs can then be uploaded to the GPS as needed. Log size does not seem to have any restrictions as to size. Tracks, waypoints, routes, logs are separate from maps and are shown on them if you have other maps selected/loaded
Hope this is of some help as I am far from an expert on this stuff and just learning the 60CSX
Good luck.
Save numerous files with up to 20 tracks tracks each, say for a given area. Each file would in turn need to be loaded back into GPS when you need it. These are individual tracks residing in a saved file. use SAVE AS feature to do this. "Tracks cannot be saved to SD card. None of this is clear or even stated in my manual.
The other option I'm working on is using track logs. Example, ride my ATV over a given area (if you go over the same ground more than once turn GPS off or track log doubles) while recording the route on the gps as I move. This data becomes the daily log (amended each time you turn GPS on and off) and can be saved to the SD card if you wish. (on 60csx at least) These logs can be downloaded to mapsource, altered, renamed, saved as different file types. There seems to be no limit as to the number of logs that my unit will hold, limited only by the space available on the SD card. Logs can then be uploaded to the GPS as needed. Log size does not seem to have any restrictions as to size. Tracks, waypoints, routes, logs are separate from maps and are shown on them if you have other maps selected/loaded
Hope this is of some help as I am far from an expert on this stuff and just learning the 60CSX
Good luck.