The pack should be plenty big - if you choose the rest of your gear well. That probably means a one-person tent (MSR Hubba, any of a number of Big Agnes offerings, a Tarptent, etc.), down sleeping bag, single-pot kitchen, and minimal spare clothing. Such selection will also hold the weight down - and I'd guess that the Z55 will be most comfortable with a load of 20 - 30 pounds.

Although I'm not trying to say my gear choices are better than anyone else's (they're not - but they're good for me), I'd be glad to send you a copy of my list if you'll PM me with you email address. I hike in the East, in conditions that may be fairly close to those you'll be in, so it might be a good starting point for you, even though you might end up making different specific gear choices than I did.