I like the 835 but it sure can be a kicker, can't it? Recoil will just wear us out. That longer barrel should help with that and you should get less muzzle whip and make it easier on your cheek as well.
You reminded me of another fatigue factor, noise. I sometimes forget that. I found out a few years ago that when I shot at the bench, if I'd use plugs and muffs, I did not get as much noise and did not get as tired. It's like being in some very loud place, even if you don't perform strenuous exercise, you can still come out and feel tired.
As you pointed out, adrenaline can certainly keep us going when we're excited about the chase and the hunt, at least for some time. Getting rid of fat, for us men, especially around the middle, and adding muscle also helps our stamina. It's the "after hunt" or "winter" syndrome of regaining the fat that seems to get to all of us, at least to some extent.
There was an excellent post on T&TH several months ago about getting into better physical shape and maintaining a level of fitness. I know that could help all of us with the fatigue factor.
"If he's out of range, it just means that he has another day and so do you."