The difference in weight between a
Karrimor Sabre 75 and the equivalent
Crux pack is 1.2 KG, the difference between the Sabre 75 and the smaller AK47 is 1.5 KG, that may not sound like much but at 30 to 40 KM per day over thirty days those extra grams will take their toll
Toughness, it's true that a lot of lightweight gear sacrifices strength for that lower weight, however that hasn't been my experience with Crux, I don't use stuff sacks prefering to kick and squeeze my gear into the bottom of the pack, if the seams were going to fail they would have done so by now. Additionally the material used is a Kevlar/Cordura weave designed to survive being dragged over rocky scree littered mountainsides and it does this well.
I purchased my first Crux pack (the AK50) in 2001, replacing it in 2003 for the newer AK47 (I replaced it because the new grey/green color was more to my taste than the AK50's dull red). In the years since the AK47 has accompanied me on some very long walks in some of the roughest country in the world.
Scallywag is correct, if you are planning on cutting down on weight, you should look to the rest of your gear too, if you want to let us know which walk you are planning then people may have some suggestions based on their own experiences on that journey.