Gotta agree with the post above. I've carried a modest camera kit on multi-day backpacking trips but wouldn't think of two DSLR bodies plus a 500mm f/4 along with camping gear. You might get away with most of that gear if you adopt a very fast and light camping kit approach (e.g. go light style simple shelter instead of a tent) but personally I'd trim the camera kit to the basics.
That said, the Baltoro 75 is a good pack as are some similar sized packs from Osprey or others but even in my huge Dana designs pack I used to hump loads on Denali and other expeditions I wouldn't dream of carrying a 500mm f/4, dual DSLRs, other lenses along with my camping gear. Have you considered renting or otherwise getting a hold of a 500mm f/5.6 PF lens, that's my go-to for deep backcountry wildlife work where I've got to carry everything along with camping gear, food, water, etc. for multiple days.
If you do decide to go deep in the backcountry with your full kit and 500mm G lens then I'd highly recommend packing the full kit including food and water and doing some test hikes before your actual trip.