the right time is the time that YOU need the advantages that full frame will bring to your circumstances, in other words if you really know in your heart that some of the low light landscape needs full frame to bring it out, then get it, after all, how many of these type trips will you make in your life, is this that "trip of ; lifetime'?, if so, and you can pay for it, get it. since this is a drive trip, surely there is space in the minivan for 2 bodies and your lens set, this way you can get the advantages of both size sensors for tele and wide. here's a valid suggestion, buy a used 5d, it's still a fine landscape camera, and i hear no rumors about a successor to the mk 2, i'm still waiting myself for that, i want the 7d af upgrade, but the 5d works as good as ever on landscape for me, so no move by me yet, and i don't feel that it's no longer a good camera. just my 0.02 as usual