I cannot compare the Garmin Edge 800 against the 500 as I don't have a 500 but I do use my Garmin Edge 800 on tour. I also carry maps. My approach is to to plan out my general route using something like RidewithGPS and/or paper maps (street or topographical as appropriate) and then I load my planned route on the Edge 800. On the road I tend to use the Garmin Edge and/or the paper maps depending on the ride. Sometimes the map is sufficient but sometimes I am going into bush areas where I may have maps that are old and the roads have changed (happened recently due to mining) or I decide to change my route on the road and this is where the Garmin can come in handy to allow me to plot a new route there and then as it can pinpoint my location (handy in the middle of the bush).

The other reason I use the Garmin is I like the numbers (data) and having a track of my ride for uploading later.

Maps are also good for the big picture/escape routes particularly on the off-road/bush tours that I like doing.

So for me there are pluses with both options and so I use both.

Andrew