I also have the 705. Battery life is an issue with any of these garmin bike computers, if you're going to bring it on tour as your bike computer, have a second computer and a map.

The mapping is useful in a city, but not perfect - I've gotten mis-routed and had to backtrack before with my 705.

I would say, if you want one of these garmins for sure for non-touring use, the 800's mapping would be a nice added benefit both on tour and for regular rides. I'm happy to have that mapping on the 705, and I do use it for regular day-rides when I'm somewhere i don't know my way around. The 500 would be worse than useless on tour, as it doesn't have any mapping, so it's just a really expensive bike computer that needs to be charged daily. Personally, if the money wasn't an issue I would choose the 800.

The other pseudo-problem I have with these things is that I'm a data geek, and if I have the garmin with me on tour I want to gather the data for all the rides so I can put it in my electronic logs (sport tracks, wko+) - so I end up feeling like the damn thing is a burden, that I have to keep it charged so I get my data. I would rather organize my tour around the external world than my data gathering requirements, so i have to fight a stupid little mental battle with myself about that. Obviously this is my problem, not garmin's.