I just feel I have register in here on your question. As others, I have no experience with the two specific packs you were considering. However, in my experience, packs are like shoes--a 9.5 D that fits like a glove for one person really doesn't cut it for another. Fitting a pack, like fitting a pair of shoes, is a very individual matter. You shouldn't buy a pack just based on general reputation. The best advice is to try on whatever pack you're considering, if possible filled up with your gear. If that's not possible, at least try it with roughly the same amount of weight that you expect to carry in it. Try walking around the store or if it's possible, around your neighborhood for a while, until you have a good sense of how the pack feels. Make sure it's adjusted properly and that it's the correct size for your torso/waste etc.

I agree with some of the other posters who've suggested that you try some lighter packs. If you wind up carrying 25-30 pounds, there are alot of good choices out there that weigh much less than the 7+ pounds of the Arcteryx. You don't necessarily need to go for the lightest out there--just try to find something that is not unnecessarily heavy for the load you expect to carry and is comfortable for you. I just settled on an Osprey Aether, if that helps give you another pack to consider. They have an Aether 60 and an Aether 70 which are somewhere in between conventional 6-8 lb packs and the very lightweight 2-3 pounders in terms of suspension, weight, and general carrying capacity.
Good luck.
Gerry Magnes
Schenectady, NY