I believe there are some other 'things' that you may wish to consider.

#1, Do you feel comfortable composing in the long and narrow confines that 4x10, 7x17, 8x20 or even 6x17cm offers. When done well, the format is awesome, but there are some serious challenges in executing to the 1:2.5 ratio's.

#2 Do you intend to shoot vistas... ie lots of 'things' with lots of little details. If so contacts become dificult and you are better served enlarging the smaller sizes or getting into the larger formats. This way the viewer can see the little things that you want them to see. Small contacts work when the subject fully captures your eye within the composition.

Since you are looking at weight, I quickly looked at the Canham specs...

the 7x17L is 10lbs, and the 4x10 is around 7-8 lbs. Not much difference there.

Holders is where you will quickly feel the additional weight. The Canham made 4x10's are pretty light (50% of a modern 8x10). 7x17 holders, individualy do not weigh much, but you put 3 of em together, in a case (see filmholders.com), and you will quickly feel the weight.

Lenses are another consideration. More lenses are available to cover 4x10, and you will be tempted to take more with you. On 7x17, the selection of 'new' or modern lenses that cover (444mm diagonal)is much smaller, and you are less likely to carry a large selection.

In summary (sorry for the long post), ask yourself how you 'see' & compose, this will help with the dimensions (both h/w ratio and size), then look at the complete package you would buy (camera, holders, lenses, tripod) and would carry. By answering these questions, your solution will then be much clearer.

Good Luck!