I show your 'calling' location as Paris, and you say you can also purchase while in the UK, so at a wild guess, would assume more of your driving is in Europe?
If so, then the way to get your best bang for the buck is to do as dhn suggests and get a European model with lifetime maps so that the most expensive of the lot is covered quarterly. You can pick up Australia and SE Asia together for about the same price as Europe.
I have ZERO experience with the latest models (not yet offered in North America), but if the GO 600 screen is as good as the Start60/Via1605 screen, it's really a winner. The Start 60 is a little more mature product, HOWEVER, it does not seem to come with a lifetime Europe map subscription if you buy in the UK (it is a Start 60 w/Europe, not a Start 60M w/Europe) , but does include the lifetime subscription (Start 60M) if you buy on the continent (???) When purchasing a Start 60, you need to be careful which one you're selecting. There's even a low end unit with only UK/ROI maps but WITH a lifetime sub.
START 60 w/Europe = £169.99 (no lifetime Europe updates?)
START 60M w/Europe = 199.95 € (has lifetime Europe updates)
GO 600 w/Europe = £229.99 (has lifetime Europe updates)