I wanted to write about this some time back, but was busy with other things. My favorite pack for the last few years has been the Zpacks Arc Blast. It's a cuben fiber (Dyneema Hybrid now) pack that weighs just 19 ounces after adding some shoulder and waist pockets. It has a 60 liter capacity, and doesn't come any larger. The pockets on the waist belt are large and easy to open and close. The main side pockets on the pack are placed down at the bottom of the pack and support easy removal and insertion of water bottles. There's a big, wide pocket on the front (back) of the pack that you can use to carry wet items or anything you want available without opening the pack.
There are a couple of drawbacks to the pack. When I've carried food for a 7-night/8-day hike, it's been pretty difficult to get the pack closed. It has velcro across both edges of the top of the bag that you press together, then roll down to prevent precipitation getting inside the pack. Even though I pack light (<12 lbs base weight), the volume just wasn't enough for a large food carry. And on that 7-night trip, I went light on the food. If I wanted to carry extra food and water, there just isn't sufficient room in the main bag.
A second 'complaint' about the Arc Blast is that the side and front pockets are mesh. They worked great on good trails. But a couple of trips ago, I encountered a lot of blowdown. I sat my pack down on one break and leaned it against a downed tree. It looked good. But there was a very small wood pick that got caught in the mesh. It tore, and since then I've had unsightly tape keeping my belongings in the pocket.
The last, and usually unimportant drawback, is the waist belt fit. If you position it just right, its perfect. But even off a little on your hips, and it's a nagging irritant. I suspect related to the waist belt issue, is the fact that Zpacks doesn't recommend carrying over 25 pounds in the pack. That's been about my maximum, with food and water, so up till now it has not been a constraint on my trips.
A couple of years back, I decided to get a Hyperlite Mountain Gear 3400 Southwest pack. It is also cuben, has about a 60 liter capacity, and has the same set of pockets--sort of. The Southwest version of the pack uses solid cloth for the pockets instead of mesh.
Up until this year, I had not used the HMG pack more than once. The main reason was that the side pockets are raised up above the bottom of the pack. The difference is enough that it is nearly impossible to get a water bottle out of those side pockets without taking the pack off (younger folks may have a different experience). If you use a water reservoir with a tube, both packs will work fine for you.
The side pockets on the HMG seem to have a little more capacity than on the Zpacks. On the other hand, the waist belt pockets seem to be smaller and more difficult to access.
On the good side, the waist belt on the HMG seems to naturally fit into the right position on the hips almost the first time and every time. It just feels better than the continuous shifting required for the Zpacks pack.
Unfortunately, the HMG is also 13 ounces or so heavier than the Zpacks. To counter this, you get a load capacity of 40 pounds, 15 pounds greater than the Zpacks. You can probably fit more (larger) water bottles into the side pockets, but you will still have the same main bag volume limit.
HMG though, is ready for that. They also offer a 4400 Southwest pack with a taller main bag that provides about a 70 liter capacity. And they advertise a load capacity of 70 pounds!
Now the reason I'm posting this on my CDT page, is that I needed to make a decision on which pack to take. The issue I have with the Zpacks is that I expect to have to carry up to 6 liters of water, instead of my usual 2 liters or less, at least for portions of the trail in New Mexico. I will need both more volume and weight capacity than the Arc Blast will provide. There may also be food carries of 7 or 8 days, and if I last longer than on the AT, I may be eating more each day. So I will need more volume.
It may be a bit of overkill, but the 4400 Southwest seems to be the only choice I have (without going to other manufacturers).
Getting to my water is my main concern with the HMG. I've tried out a couple of solutions. One was an Evernew drinking tube that fit on their bottles, and other bottles with similar caps. I could use the tube from a bottle in the side pocket. But I really don't like tubes, and filling up a 1 or 1 1/2 liter bottle frequently with the weird tube caps would be a bit of a pain.
The alternative is to use a 16 ounce water bottle in a holster/pocket on the shoulder strap. I will probably have to take the pack off to refill it, but maybe not any more than I would for short breaks. I will have to change from using one of those shoulder pockets for my Steripen, but that's not a big drawback.
So while I could probably make my Zpacks work for the CDT, I'm going to go with the HMG to give me the margin I desire to carry more water and food.