What Glen said.. if you are making relatively light gear choices there's no need to add 3+ pounds to your load with a huge giant pack. (unless you are also planning on taking up rock collecting on the trail or bringing 30 pounds of clothing and crud with you).

Not to discount salespeople who can be very helpful, but often I find that outdoor retail people tend to "upsell" newbies a lot, and since the expensive stuff is either the large "expedition" things or the hyper lightweight uber technical ultralight stuff, the nice stuff in the middle that is well suited to most hikers often gets ignored in favour of buying
something "bigger and more durable" (I've never worn out a pack yet..)

I would suspect you should be able to get a pack that will fit you well and be comfortable with a lighter load that weighs around 3 pounds. The choices Glen has mentioned would be the same places I'd point you at to start. (I have a Granite Gear bag myself, and I've had lots of freinds very happy with the
Gregory Z packs) If you were shopping with me I'd drag you into the local store and make you walk around for half an hour with a Gregory Z55 on your back with 25-30 pounds of weight in it.