Hope this input is not too late. In reading you post, I wasn't sure if you're looking for to just make larger prints or “absolute image quality” in large prints. I also wasn't sure whether color or B&W is your primary medium. My experience and the other photographers I backpack/travel with is with color transparency film capture, scanning and digital output (LightJet, etc.).
For my landscape work, I use Hasselblad and 4x5. I find myself using the 4x5 more because of the flexibility (movements, QuickLoads, ReadyLoads, etc.). A couple of my buddies that I travel with use 5x7 and 8x10. However, I notice they are using their 4x5s more because of the ease of use with QuickLoads (pre-loaded film and a holder). They have separate backpacks for 4x5/5x7 and 8x10. Let me tell you, the 8x10 backpacks are big and heavy, once you start putting 4-6 film holders in there.
For absolute quality, one of the guys will shoot 5x7 or 8x10. When you see a 30”x40” or larger print from 8x10, it is pretty amazing, but a costly endeavor ($100 for the drum scan/$100+ for printing). You can still get 8x10 Velvia and Provia from Japan, but it is over $300/box. Shooting 5x7 and 8x10 is a labor of love and expensive. The film [color transparency] is getting harder to get and you end up having to order it directly from Japan through a dealer who will help you do that.
Shooting 4x5 will get give you the ability to make larger prints, do panoramas (2.5x5; 2x5 film size when cropped), etc. You can put an entire 4x5 field camera 2-3 lenses, light meter, film, loupe, etc. into a “technical pack” and pack all day with it easily. If you want to do 5x7, Canham makes a 4x5/5x7 camera that will do both—you have to watch your lens selection though, some reasonably priced lenses don’t have a large enough image circle for 5x7.
Bottom line [for me and the way I shoot] is that I find a 4x5 field camera is a good compromise between “absolute image quality” and convenience. QuickLoads (Fuji)/ReadyLoads (Kodak) are great, because you don’t have to spend the evening loading film after dinner! QuickLoads and ReadyLoads cost more than sheet film, but I find the convenience welcome.
For proof prints from 4x5 (up to 16x20 and possibly 20x24) the Epson V700 scanners work well—just ask Charlie Cramer, I did. As one poster indicated, the Hasselblad/Imacon Flextight is excellent. One of my buddies doesn’t send any scanning out anymore for his 4x5. He just uses his Imacon FlexTight. If you go larger, 5x7 or 8x10, you are either going to have to buy a larger and/or more complicated scanner or send it out.
Again, these are my experiences from shooting: color transparency film, scanning and digital output. Hope this helps.