The more I follow, what seem to be endless threads on this subject, the more frustrated I become.
See this forum: http://www.ukgser.com/forums/
The bottom line, as far as I can see, is that there is no gps unit that can upload great quality maps for use everywhere in the world.
I think I am right in saying the great maps are available but can not be uploaded to a garmin. They can be uploaded to a laptop PC. Then a fantastically complicated, to my mind, software prog is needed. This software allows a gps to be connected to the PC so that a real time position is shown on maps displayed on the PC.
I think I will use a gps with the best uplaoded maps available and printed maps and maybe dowloaded maps and forget the gps/PC interface software.
The software I looked at was oziexplore. More like ozipullyourhairout given my desire for a low tech life.