My primary distance pack has been a ULA-Circuit; it's held up well and doesn't allow me to overpack. The only problem at times is weight capacity. You're lucky to be near a Cabelas and REI, as you can actually haul your gear down and load up a pack to see how well it loads and fits. One thing to pay attention to other than pack capacity, is the rated "comfort weights" which identify the limits of pack weight for the rated suspension system...that's important. My ULA is awesome, but the "comfort" rating tops out at about 30 pounds; if I push it over 35 pounds, I can feel it.
I'm actually going to try a new system this spring. I've went to the higher end with Seek Outside packs. They are a hybrid system that actually have an external frame. I have the 4800 liter Unaweep and a smaller backpacking 3500 liter Gila pack that I can swap with the frame. Now, my base weights are typically between 12-16 pounds depending on season/shelter-system. I can normally do a 5-7 day hike and keep total pack weight under 30 pounds (includes 2-3 liters of water, food, and fuel). Some locations require more water capacity and longer trips without resupply also add more weight than bulk...those push the limit of my ULA pack. The Seek Outside pack frame/suspension system is designed to carry over 100 pounds...and it will. Weight is weight and sucks beyond a certain point for most normal people. Not that I want to pack more weight, as my goal is to continually trim when and where I can; however, there are times when you need to tank up on more water and more food, which is what affects my pack weight the most. I haven't been able to test out my Gila yet, and will next month for a 105 mile section hike, but I've done some road-march training (the best I can do in Afghanistan) with the larger 4800 pack, and carrying weights up to 65 pounds is far more comfortable than it has any right to be.
This hybrid external pack frame and suspension system is quite unique, and it works as advertised. It also gives you a lot of additional mobility the way it's designed. Just some feedback as I looked for some certain pack requirements. No one pack will be able to do everything, but a good pack will cover a wide spectrum of activities and seasons. My ULA-Circuit is by far my favorite pack for about 7-8 months out of the year, but it requires pretty strict pack weight management and limits me from doing longer trips (without resupply) or where I'm required to carry more than 2-3 liters of water.
Your pack's capacity and weight-ratings will depend highly on your kit contents. You'll need to measure the bulk and weight as you search for a pack. As many said, make sure you get measured and fitted properly; that makes all the difference in the world when actually using the pack and knowing how it should feel. Don't get too large a pack as you'll end up tempted to fill it up; however, some expansion capability really helps when you don and doff layers.
Pack weight is one of your "top three/four" items that make up the greatest amount of your weight. Frame/suspension is important, but I've been moving away from the larger 7-8 pound packs over the past several years. I do look at pack weights and try to keep them to 2.4-3 pounds. There are some ultralightweight packs that have no frame and weigh 1-2 pounds, but they require extreme minimalism and discipline to keep base weights well under 10 pounds and fully loaded weights 15-20 pounds...God Bless'em! The good news is that several companies make reasonably priced packs that are lighter and still capable of lightweight loads (25-35 pounds). Some good links above with ULA, Osprey Granit Gear, and Gregory. Next tier up get into the Seek Outside price range, but they're a little more niche for their capabilities.
Pack features are highly dependent on the user. Some like multiple pockets for organization which adds more to the overall pack weight and bulk. If you're disciplined, a more streamlined pack will be lighter and less bulky. I like the larger side/bottle pockets, especially with the smaller main-compartment packs like the ULA-Circuit. Additionally, I like an outer mesh type pack for storing my rain fly if still wet, along with my water purification system. While I do like a top lid pocket, it's not a deal breaker for me, but it does add extra weight. I also like larger hip belt pockets. I don't carry much in my pants/shorts pockets and nothing on my pants webbing belt, so those pockets are my "EDC" item pockets (as is my HPG Kit Bag, but that's for another topic). I can carry almost a day's worth of trail snacks in those pockets, hand-sanitizer, and mosquito repellant. I use a water bladder, so most packs now come with a port for the hose. Compression straps are important. If you're pack is not fully loaded and not compressed, it will flop around and drive you nuts.
Just a few thoughts on this wonderful morning in Afghanistan

:
ROCK6