For what it is worth-
My first choice for remote travel, mf would be a rollei in good shape, but you give up interchangeable lenses.
If you need interchangable lenses, and the mamiya 7 is too expensive, I would go with a 645slr.
I have been shooting a pentax, with a 55 and 150 lens that makes a very nice travel kit. Really no bigger than a 35, with much improved image quality. The pentax is battery dependant, so if that is a concern, get a mamiya.
As to the format- you will be told and read all sorts of stuff, lots of which is really nothing more than urban myth. The pentax was my first foray into 645. Prior to that I have shot everything from minox to 8x10, and my take is that contrary to what others may tell you, yes, you will see a big difference between it and 35. The old adage that bigger is better may not always be true- there are all sorts of factors that impact image quality, format being just one.
When I got the pentax, I did a little test. I shot the same scene, with three cameras, the pentax 645, a pentax 67 and a 4x5 with 150mm ektar lens.
I used the 55 on the 645, a 55 on the 67, acros in the mf, and trix in the 4x5. I shot the same scene, on a big zone VI tripod, using shutter speeds of 125th second or more. The tripod was moved to get the same framing in each.
What i found was that with full frame 11x14 prints handed out to a bunch of friends, there was no difference that anyone could see. I cranked my d2 enlarger as high as it would go and made some more prints. Both the 67 and 645 were sharper than the 4X5. Again, very little if any difference could be seen between the mf images.
My take is that there are all sorts of factors- film flatness, lens quality, film ability, vibration, that affect the ability to give a high quality image.
A really good 645 is going to give better images than a mediocre 6X6,6X7, or 6X9, and maybe even bigger.
What you want is a camera that will hold the film really flat, not shake much, have the best glass available,be light enough to carry around, and not die in the middle of nowhere.