Buying a new pack: Gregory Z55 vs Granite Gear

I have owned the Z 55 and tried the GG. Frankly… For what you are looking for. You are in the wrong ball park with the Z-55.
The Z-55 is a good pack. But it is heavy with to many "parts" that you won't use. It could have easily been a pound lighter without so many dang zippers. Though they did fix the strap problem, I think.
The Granite Gear is a good pack. Its lighter and still has some kind of a frame. Both are just as durable as the other. In fact I would lean toward the GG. It has a larger volume. And you will want all the flexibility you can get with your "todo list". Packing the GG right takes some getting used too. But its worth it. Your back will thank you.
Along those lines is the GoLite Pinnacle. Great pack. Easy to pack and very adaptable to changing situations. All three are bomber made (assuming Gregory fixed those strap blowouts). But overall the GG is the better choice for what you want. As for the price. The GG can be found cheaper. And the smaller Jam2 is only $100. As are most frameless packs. Look at MLD, Gossamer Gear, Six Moons Designs, and GoLite. You DON'T need a frame to do what you want. Especially under 35 lbs. Just my two cents… Hope it helps!!!

-Passionphish

IMHO, you need to first determine the max. load you'll carry, both in terms of weight and volume, then go pack hunting.

Mountaineering typically requires fairly bulky and heavy loads. I don't think either pack you're considering will work well under the conditions you're looking to cover.

I tried the Vapor Trail, and found it uncomfortable for a long haul with anything over 25 lbs. 25 lbs is an easy weight to hit for 3 season trail hiking, but when you start adding rope, biners, crampons, and an ice axe, that's going to be a hard weight to hit. Also, I think you may end up shredding this pack as the materials are pretty whimpy for mountaineering.

The Z will probably handle the load you're going to haul, but volume is limited (3350 c.i. at 3 lbs 5 oz., Gregory claims it'll handle 35 lbs.). By the time you add the above, cold weather clothing, and a winter bag into the mix, I'm not sure this bag has enough capacity.

My current go to pack for winter and mountaineering is the Osprey Exposure 66. It handles a heavy load with ease (I've pushed it to 35 lbs on a shakedown hike over a short two day 22 mile trek – at that weight there is complete load transfer to the belt…and I haven't had the belt custom molded), and readily accomodates changing load volume (like when you consume food, switch out clothing, etc) via a great compression system. The Osprey isn't light weight (3 lbs 15 oz.), but the addl 10 oz. over the Z gives you lots more flexibility (4000 c.i., lots of places to store your snow tools, heavier load carrying capacity (osprey says 45 – 60 lbs, gregory claims up to 35 lbs). I'm so happy with mine, that I'm not even considering anything else for these kinds of trips.

I think someone had one for sale on this site earlier this month for $150. It might be worth checking out.