I would be more concerned with weight than which camera since carry on weight limits keep dropping, particularly in Central Asia and South East Asia. Are you taking any domestic flights? That might be a sad end of you camera and lenses if you are required to check it at the gate. My bag with just a few lenses and two bodies prevents me from flying quite a few airlines, especially the cheap one would like to fly.
As a counter point to Howard's well reasoned warning about taking a new camera on an important trip, I would submit that my D800 had less than 20 clicks on it, and the manual was still in its plastic, before heading to Scotland last May. It was an important family event with my sister and me meeting in the Lake of Menteath area to spread our parents ashes in the lake which was our ancestral home. So blowing the photos was not an option. The results; could not be more thrilled. That one trip got printed large and hung more than any of my prior travels to 86 countries. The camera is logical, reasonable and great with easier metering accuracy, easier color, easier AWB, easier better AF down to true dark conditions, and HDR like DR if one wants to boost what seems to be the limitless recoverable detail and color in the shadows. It is not a point and shoot however, it helps to have a background with all manual film where the fundamentals are paid attention to when setting every shot up. I still have not read the manual, the first product I can remember for which I didn't. I like manuals, the more technical the better but just never needed to with the D800. The camera is not that much different in operation from your other cameras, just the results are so much better.... There were a couple points that caught me by surprise such as the inability to use trap focusing, or VR starting with AF-On but that latter one was a welcome change.
As I mentioned, I would be more concerned with your carry on weight than which camera and lenses you take. Stan St Petersburg Russia