If your looking for 2-up, comfort and reliability, I don´t think you are limited to 1000cc/+ bikes these days. 650-800cc could also do it (I do admit though, that 2-up is the part, that´ll narrow the choices down in the middle class considerably).

There are other points, like weight, fuel consumption and fuel range, that might be in favor of a smaller cc bike. Power & torque is not really a problem with them any more, as engine management systems have evolved so much.

Plus it´s very hard to find any comprehensive insurance, that´d cover your bike everywhere in the world, so you risk losing it completely, and without any compensation, on a trip like this. Its value might also be meaningful, it you will need the carnet on your trip (this depends on your choice of routes). And it´ll gather new scratches at an alarming rate on a trip like this, so price depreciation will be rapid, even if the worst doesn´t happen to the bike. All aspects, that are against buying the newest, shiniest, and most expensive tourer you can find (but you probably weren´t going to do that anyway - will leave out at least the Tiger1200, because it´s new for this year).

edit. But bikes do not cost the same all over the planet, over here they´re pretty much as expensive as they get, so getting wear and tear quickly, or the possibility of losing the whole value of it might not hurt you the same way.