A pile of panniers could be on the ground in two minutes. Good idea.
I use the stoney point tripod with the extra attachment to support the butt, for sitting shots. This can be steady enough for an 800 yard shot. But, takes practice to use and set up. Take a look at these. I've also used my spotting scope tripod with my backpack for a rear rest. This is even better, but takes more time for me to get to. I think the rope around your knees would be a big help too.
Had the same situation happen on the deer hunt. Uphill 30 degrees at 1069. I tried, but the deer was standing on the skyline before I got all settled. In the end, I just watched him dissapear. Looking forward to hunting him this year!
In my string, I've got two that'll stand quiet for shootin. They know what's comin', and will even back up a few yards. Then there's the rest... Actually had that work out for me once. I was waterin' Rusty at a creek when I spotted a coyote about six hundred yards up the draw and comin' down. I crawled up on a little ridge and waited. When my first shot missed the horse and the dog broke left. The coyote stopped because of the horse, and turned around, coming back to where I'd missed the first shot. He caught the second.