I used the Southwest 2400 on a three day Lean-to Rescue. I carried my normal 20 pounds plus about 30 pounds of various tools. I experienced next to no pack collapse at 45-50 pounds. I was surprised at the testing. The pack held solidly onto my hips and fairly lightly on my shoulders, even with the weight I was carrying. Of course hammers, saws, nails, prybars are dense material, mostly. I packed them lower in the pack, just on my compression pack with cloths/sleeping bag. I am not sure I agree with the collapse test. A lot depends on where and how high you pack the main load. Packing heavier stuff high would lead to more collapse onto your shoulders, I think. The shoulder straps did bite into my shoulders somewhat, but this was more because they are narrow and heavily padded (2-3/4″ wide, 3/8″ foam.) A wider strap would have prevented this, I believe. A 3-1/4″ strap works better with heavy loads. But, I was 10 pounds over HMG’s maximum weight anyway.
I removed the extra buckles, side tie-downs, etc. It is under two pounds today, despite the heavier black fabric. Still too heavy for general backpacking, but a nice pack for the L2R projects.