There are a zillion variables to consider, and it helps to remember there is no good way to light-backpack with a dslr kit.

Camera and lens(s)? e.g., a 5D and an E-420 are worlds apart and present very different challenges.
Fast access? Do you want to alway be able to retrieve and shoot on the fly, or do you shoot under carefully planned conditions?
Support? Do you carry a monopod or tripod?
Anticipated conditions? Chronic rain and snow? Blowing dust and 110 degrees?
Other gear carried? How much backpacking base weight and supplies? What is the backpack's overall design?
Trekking poles? Using these affects some camera carry options.

I generally only carry a dslr on day hikes because I can't seem to accommodate a lot of bulky, heavy gear on longer trips. I'll probably build a mirrorless system and revisit the whole question.

Cheers,