40x60?? Extreme in the other direction - two orders of magnitude. Even a D800 only is 18x12 or so at native resolution, so you're going to be doing upres no matter what you do to get to 40x60. If you're really going to make that many 40x60's, you probably would do well to get a D800e, even if you're going to sell it at the end of the trip. My first thought was renting it, but it's a three month trip and the rental would probably be equal to the purchase price. But you'll also need to look into something like BlowUp or other similar software.
You must have a big room if you've got space for 5-6 40x60's...
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!