Running the John Muir Trail and Climbing Cathedral Rock
Both have their pluses and minuses and if you have a variety of interests and your endeavors are of varying lengths I recommend having both in your pack arsenal. However, below are some points of comparison that can help you choose the pack that will work the best for you if buying both is not an option.
Ready for adventure!
Capacity:The Fastpack has more than double the capacity of the PB Adventure Vest, yet it weighs in only at only 3 oz more! It's a no-brainer really which pack to use if you need to carry a lot of gear. I used the Fastpack on both my JMT FKT attempt as well as on a multi-day peak bagging expedition this summer.
At the start of the John Muir Trail and on Lost Peak
I've also used it for several rock climbs and technical mountain ascents where I needed to carry a helmet, crampons, rope, harness, etc. The Fastpack easily swallowed all of it.
Rappelling on Cathedral Rock
I've found the PB Adventure Vest to be optimal for day long self-supported expeditions. I've used it on multiple 50-60 mile runs in the mountains throughout the summer as well as some less technical climbs. The capacity is ample for carrying plenty of food and water as well as extra layers and emergency overnight gear.
On the go hydration refill
Summit of Black Peak
Running through the North Cascades
External Lashing:While the Fastpack has two ice axe loops, making it more versitile for technical equipment and stashing poles (whereas the PB Adeventure Vest only has 1) it lacks the exterior bungee cord of the PB. The Fastpack does however have a large mesh pocket on the back of the main body which is an excellent place for a minimal shelter. In all, I would prefer to attach stretch cord to the outside of the Fastpack as well since I use it for strapping on things like my helmet.
Summit of Blackcap
Front Pocketing:Pockets are the crux for me. Seriously. I am someone who is almost continuously on the move. I want a lot of accessible pockets up front so I can eat (apply sunscreen, check my maps, take pictures...) on the move (or at least without taking my pack off). Here is where the PB clearly outshines the Fastpack in accessible storage.
The front pockets of the PB can carry 20 oz bottles, or you can stash other things in them if you're using handhelds or a hydration bladder. Each of these bottle pockets has 2 small stretch pockets on them. These are perfect places for gels, bars, or Chamois Butt'r packets, or your sunscreen, hand sanitizer, lip balm, etc. The Fastpack has the two bottle pockets, but only 1 subsidiary pocket on one of the bottle pockets
One more note on the bottle pocket, The PB has little leashes to go around the bottle tops. This keeps them from creeping up and out as you run. I had to keep pushing the bottles back into place on the Fastpack because it doesn't have those.
Below the bottle pockets are smaller pockets. The ones on the PB are tiny. Good enough for electrolytes, a car key and some Aqua Tabs and not much else. The ones on the Fastpack are much larger, so that's a nice addition.
Moving up the shoulder strap the PB has two large zippered pockets. I have crammed my phone, baby food pouches, Trailbutter pouches, gazillions of gels and bars and who knows what else in here. It's also where I normally store my compass if it isn't around my neck. These vital storage spaces are not on the Fastpack. Despite the larger pockets below the bottle pockets, adding these to the Fastpack would be an excellent use of that otherwise blank terrain on the shoulder straps.
One other pocketing note. The PB has a velcro closed pocket on each side between the body of the pack and the shoulder strap. I haven't used these spaces often, simply because I don't usually need them and I'm never 100% sure I trust things not to fall out. However, I have stashed some bulky, yet light food items there (baggie of Snappea crisps or Dang Coconut Chips). They have been totally secure and comfortable. I was even brave enough to throw my jacket in there the last time. There is a security loop in there that you could clip or tie a valuable to for extra security.
PB's side pouch
On the other hand, the Fastpack has large, stretch slash pocket on the sides of the body. You can put a water bottle, layers, or food in there and they hold a LOT. These make up for the missing smaller pockets, however, I don't find them as easy to access as the pockets in the front. The other thing about them is that they don't close like the pockets on the PB do and so I'm always afraid of things bouncing out, getting snagged and pulled out, or getting lost if I take a tumble.
Packing for the JMT
Fabric:The fabric of the Fastpack seems more durable than that of the PB. The stretch mesh used on both packs is tougher than that I've had on some of my backpacking packs and I appreciate that when I'm bushwhacking! I like the feel of the PB against my body more than that of the Fastpack.
Weight:As I said before, the Fastpack only weighs a few ounzes more than the PB and has much more capacity.
Comfort:The comfort of both these packs is top notch. I've had them both maxed out and run double digit mileages in them. There's no ride up or awkward swaying. The PB seems to wick better and when not stuffed to the gills is practically unnoticeable. The Fastpack, since it is larger, covers more of your back and doesn't seem to wick as well which can be pretty slimy and sticky when it's hot and humid. That could also be due to the built in padding in the back of the Fastpack. The only time I've had any discomfort in it was when I had 4 days worth of food, several liters of water, and full backpacking gear inside. My shoulders were achy by the end of the day. However, that's a pretty extreme load for a running pack.
Running the JMT