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.