I may be going on the same trip...let's see if I can help a bit:

Backpacking a hiking tour in mountainous areas is vastly different to backpacking around Europe by train...are you likely to be carrying gear 2 miles or 20 miles a day?

I'm thinking he said 15 to 20 and the terrain is mountainous and remote.

Are you going to be in relatively safe areas where you'd be comfortable enough to use an obviously expensive bit of kit without worrying about someone mugging for it later, or are you likely to need something a bit more discrete?

Between the small villages in the mountains of China, there aren't too many people...I don't imagine theft prevention is an issue.

Are they purely for personal use for the family web album? Or are you intending to blow some of them up to A3 size to use in a presentation.

Being a missions oriented trip, I'm sure there will be presentions requiring enlarged photographs at decent quality as well as slide shows on digital projector. These photos will need to be retouched in Photoshop. Definitely will also be used for personal albums as well.