Each person's mileage may vary as to exactly what is too heavy. Generally speaking, I'd say if you've got a 10lb gun you love and you're not doing this kind of hunting as a super regular thing, I'd say suck it up and carry it. It won't kill you. If you're going to do a whole ton of this kind of hunting (or just want a new rifle!), then I bet you'll want something lighter for the longer run. I also don't think twice about barrel length; have hunted with guns anywhere between 20 and 26 inches, and never once did the barrel length bother me in any way.
For me, weight classes are as follows:
Over 10lbs (but under 13 ish) is doable, but I expect you will be thinking 'damn, I need a lighter rifle' after dragging that that up/down a mountain a few dozen times. (over 13lbs, I don't know If I would even think about dragging it up a mountain).
Between 9lbs and 9.9lbs is more doable, and you'll make a few more trips up/down the mountain before you start thinking 'damn, I need a lighter rifle', but you'll eventually decide you need a lighter rifle.
Between 8lbs and 8.9lbs is getting into a weight class you start saying to yourself 'hey, this is pretty OK, a lighter rifle would be nice, but I could live like this.'
Between say 6.8lbs and 7.9lbs is the neighborhood you think to yourself 'wow, this is a sweet little mountain gun, I love this thing.'
Get much under 6.8lbs in any of your usual 'big game' cartridges, and you'll starting thinking 'Wow, this is super super nice to carry around, and this is also a pretty uncomfortable amount of recoil.'
YMMV.