If you have a spare M body take the Leica with a couple of lenses plus a spare body. The last thing you want is for the camera to die in the middle of your trip. Of course if you have a spare Nikon that becomes an option too, though a small fixed lens camera could work as a back up. Me I would take a medium format, probably a Yashicamat and a Fuji 645 as the latter weighs less than a lot of 35mm SLR's with an Oly OM1 for speed and fun shots. I can't travel with one camera even though I end up nearly using just one.