The 705 is the dog's b0ll0cks - does everything you could dream of...
It really depends what you want out of it. If you want mapping or heart rate, you're looking at the 605 or 705; if you want cadence, 705.
For touring, it probably boils down to the length of your tours and how much memory the unit has as standard if you can't download it every night - the 705 could probably record several thousand km with an extra card.
As I think jimboalee has also shown, the battery life of any unit can easily be extended with a Power Monkey.