Is the extra capacity of the Bora 95 over the Bora 80 worthwhile? I have a daypack so I plan on using this one as a multipurpose pack. I recently took a 3600 cu. in. up Rainier, and needless to say it was grossly insufficient. I don't mind spending the extra $50 on the 95, but is it too bulky for mountaineering or worth the investment?

Have to comment on the Himalayan trek comment, or at least clarify terms. While there is opportunity to do expedition backpacking in Nepal, the traditional trekking routes are less than wilderness conditions. Most people would be hiking from trekking inn to trekking inn, sleeping in a bed and room that is spartan and smaller in comparison to the typical jail cell, eating from the same menu that the inn had last night, and will have tomorrow. You don't really need a guide, just follow that path, but I hired a guide for safety as I was alone. His equipment was a change of clothes carried in a pack you might see between classes on campus. I could expand on the reason for this, but I had the Bora 80 and it was way overkill.

If you really need a massive mountaineering pack I would recommend the Gregory Denali Pro, it is the gold standard for high capacity, comfortable do-anything rig. I run a Bora 65 for my regular backpacking trips and it can easily do 4-5- days at full capacity in late season, the 80 is absolutely plenty of room for anything short of a Himalayan trek. Of course the main principle is that any capacity/structure you don't use is excess weight you don't need to haul, so plan accordingly. If you are a serious hiker/backpacker it's worthwhile to invest in 3-4 different packs for whatever your needs may be on a given trip.

Brandon is right about the Bora 95 being HUGE. Even the Bora 80 is a big pack, and maxes out around 92L in the tall model. I can honestly say that when I got my 80, I also tried on the 95, and immediately knew it was much more than I wanted to carry, both in terms of its size and the load it can handle (and I came down from a 100+L Jansport). For years, the 80 has easily handled many a trip of a week or more without any regrets from me. It's also incredibly comfortable with 50lbs or more on, as well as being virtually bombproof in its materials and construction. Good mountaineering pack, worth every cent.

The real question is are you going to carry that much stuff? The Bora 95 is HUGE! Like, double the 3600 you carried. If you're going to be carrying massive loads, the 95 is your rig, but most trips, even extended winter trips, should be accommodated by the Bora 80. Remember, you will always fill your pack, no matter how big it is...