For me, a 400-700cc bike would be just about optimum for riding solo, some people prefer even smaller, like 250cc.
A 1200cc bike is of course very comfortable on the big highways, but quite heavy, and expensive to buy. Could also affect your carnet bond amount. Complicated technology could be hard to repair in the middle of nowhere. A big bike is also a bit more expensive to send as freight.
And you´re probably unable to get comprehensive insurance for the bike for a trip like this, so you could lose it completely, and get no compensation from your insurance company. That´s also something to think about – could you afford to lose a 1200cc, if not, then maybe go for something cheaper?
Just my 0.02.