i use a vista c, now cx, with city select mapping. it shows you where you are, all the roads and theres a postcode finder/street finder option which will generate a route for you to follow with full turn by turn insructions before every turn.
i use tracklogs digitalmappping(OS) to plan rides before downloading to the gps.any points of interest on the ride are saved as waypoints and the ride planned around them.
using tracklogs to plan will let you follow any off road tracks.
it isn't cheap to set up though!