Hi:
Firstly
My philosophy on this is that there's no such thing as a perfect adventure bike, so ride what you have, ride what you love, ride light and ride cheap...
Think hard about what you want to do with your steed because every choice you make will entail a compromise of some sort. If you don't already have bikes, try some and see what you do like. If you're doing any challenging off road riding, buy a bike that's light - compromise the least on weight. Even if you're only doing 5% off road, they'll be the toughest parts, so plan for those parts. Remember that nobody wishes their bike was heavier - EVER! (Keep the luggage to a minimum too). Don't let your choice of bike ruin your trip... i.e. don't let the mistake of getting a big bike limit where you can go.
Don't buy an expensive shiny bike, instead, buy cheap and put the money into the travelling. The same goes with modifying, don't over do it, save the money for the travelling. Most bikes can do everything you ask of it, some are better suited to certain things, but as a general rule lighter is better. Try and make a rational choice and avoid the pull of the 'adventure' industry and the marketing designed to sell you heavy bikes and all the must have gadgets.
These are the mistakes most first time moto-adventurers make, myself included.
So, IMO you should consider bikes around the 140kg mark, that have around 60bhp, you won't need any more power, bikes that are in the 250 - 400cc range like the XT250, TTR250, WR250, DR350, or DRZ400...
Bon Voyage.