a lot depends upon time of year, if it's in the winter you need more clothing and a warmer sleeping bag, hat, gloves, long johns, etc. (so more room in your pack).
Also depends a bit upon where you're going, because some national parks in California require bear canisters, so your pack needs to be large enough handle those.
Also, hiking in alpine meadows at 10,000' is much colder in the summer than hiking along a beach.
All that said, I used a Osprey exos, 58 Liter, 2.7lbs, great harness system, especially when fitted properly by REI experts in store. It has met all my needs, even in winter conditions. But, I probably would have a very tight fit if it was dead of winter, 5 days, with bear canister.
Bottom line, I recommend a 58liter pack. I would not go lower unless you're prepared to spend a bunch of $$$$ for ultra light stuff.
Just looked at that pack, YIKES! Super expensive, one of the heaviest! Only a 45 and a 70 liter version!? Probably intended for heavy duty climbing, where you need an extremely durable and roomy pack.
@bop Thanks for reaching out!
@Philreedshikes gives you a ton of great info in his post so we won't repeat here. If you're backpacking for five days with everything on your back and no resupply, you will likely want to go with the 70 liter version of the Osprey Archeon Backpack. If you've got your kit dialed and it's very light and small you may be able to make the 45 liter version work, but that would be pushing the limits for that length of trip.
Hope this helps, enjoy your hike!
Why the Archeron? It seems to be more a travel pack than a "hiking" pack though it is clearly a hybrid. The guide load range is 25# to 45# which is quite low for a 70 liter pack and since it is a ~5#+ pack that tells me it may be oriented towards air travel where the max weight is typically 50# possibly accounting for its flatter simplified externals.
For wilderness backpacking the Aether or Atmos lines might be better starting points if you like Osprey but it does depend on your plans. The Archeron may not be that comfortable if you hiking any distance.
Certainly it is hard to pin down a recommended capacity for something as vague as a "5 day hike" since that depends on whether you are camping or staying at hostels and whether the time or location requires special gear. Winter, altitude, latitude all may require bulky cold weather clothing.
Whatever, I would recommend visiting an REI store or similar and getting fitted.