Osprey Aether/Crescent 70 vs 85 for Mountaineering

hi,
this summer i'm planning to get into mountaineering and i'm doing an alpine school with Mountain Madness to the Northern Cascades at the end of august. Since i don't have any gear, for the last 2 months i'm spending tons of time reading reviews and researching every single piece of equipment required for the trip. One of the big purchases is a backpack, so far i narrowed my research on Osprey packs and hit the bummer. I'm 5,7 at 145 pounds guy. I really want to get into serious mountaineering and decided not to be cheap on gear since i'm buying it for a frequent use.
Currently i'm deciding between two models and two weight capacities:
Osprey Crescent vs Osprey Aether
and
70 liters (4500 cu in) vs 85 liters (5200 cu in)

crescent has more options, but heavier than aether. aether is lighter but less 'sturdy'.

with sizes it's also confusing, several people told me that since all my gear will be new, it will be lighter and more compact, so i can get away with a 70 liter pack (4500 cu inches).
but on the other side, you can't make a pack bigger, but you can definitely make it smaller.

can you please share your thoughts and experiences to help me make a choice,

thank you in advance,
andrei

Actually, this belongs over in Climbing, rather than Backpacking.

Aside from the fact that I would have chosen one of several other guide services to learn basic alpine stuff than MtnMad, the basic question is what you have in mind beyond the basic and advanced alpine courses. Are you headed for the 7 Summits (guided by MtnMad?), climbing with your buddies on Cascades peaks, climbing with your buds in the Andes, or ? If you are headed for a 7 Summits quest, then you will need at least a 5000 cu in pack very quickly. If you are doing the Cascades, Tetons, Canadian Rockies, BC Coast Ranges, and that sort of thing, 4000-5000 is just fine. If you are headed for winter backcountry ski tours with climbing, 5000+ and a sled for hauling are needed.

I use a Dana Terraplane for my expedition and winter backcountry ski trips (5500 cu in) and an Osprey Aether 60 for things like Sierra, Rockies, Tetons summer backcountry climbing trips and weekend backcountry ski tours. Note that the breakpoint is up to 4 days for the Aether and 4 to 30 days for the Terraplane, with some adjustment for short trips that involve lots of technical climbing and long trips that are basically scrambles with little need for gear beyond a rope and a few chocks and cams.

The Aether is very light for its carrying capacity in all capacity ranges. I would not consider it any less sturdy for the loads you might carry. The Dana (the current owners still produce the Terraplane and Astroplane) is virtually bombproof for rough handling, but is really heavy, over double the weight of the Aether.

Even for mountaineering trips, you can reduce the load you are carrying. For example, my winter/expedition bag (from Feathered Friends) is only a couple pounds heavier than my 3-season bag, (-40F vs +10F). On expeditions you double up on your sleeping pad, but adding a closed cell foam pad for the second pad (the generally preferred option) only adds a half pound (a third of the 3/4 length Thermrest most people use for their primary expedition pad). A lot of the stuff is the same - same stove, same cookpot, same cup/bowl/spoon, most of the same clothing, same camera (or a smaller, lighter one).

The big question, though, is what does MtnMad recommend? If you show up for your course with gear they don't list or that is equivalent, you might have to buy replacements on the spot (REI home office is in Seattle, plus most guide services running training courses sell or rent major gear items like packs - which is an alternative, rent before you buy). They should have or soon will send you their suggested gear list, plus they have a "gear guy" for you to call for advice.

Best if you can get away with a smaller pack for your mountaineering endeavors, or carry a separate summit pack or contrive using pack lid as waist belt (hint: keep belt packs clipped to something while climbing).

A 50L can be good for several days or more with all your stuff, and is still small enough to be comfortable for climbing. 50L = 3000 cubic inches. I've also found a 4000 cu incher a few times OK for climbing, but anything bigger becomes inconvenient on technical terrain. I carried a mostly empty 7000 cu inch sack on a grade III+ Cascades route and found it annoying and regrettable hindrance, though not bad for approach.

I bought an aether 85 and I feel it was a good choice. I had all the same things in mind. The aether compresses very well so you should not worry about the empty space. I'm using mine for the JMT next year and I got one of those wild Ideas 10 day bear canisters. It takes up most of the space in the pack. I'm glad I have the space.

The thur-hikers will tell you to go smaller and lighter, but be sure you're ready before you do. I've run into many people who have adopted some of their tactics, but not their abilities. These are the people limping with running shoes and small packs.

I just met a number of thur-hikers on the PCT who were on mile 900! I was impressed, but also recognized that I am not in their class. I prefer taking a few fun items (fly fishing gear, booze and good food.)

Greg