I think the beefier stays will be necessary to carry the heavier weights the pack is, at least in part, designed for. I'd say the typical 20-25 lb max loads most BPLers carry are probably ok with the current stays, assuming the pack is properly filled. I found it to carry far better with the load filling the pack to at least the top of the stays.
On the recent ULBC trek, I had a base of about 9 lbs and carried little water. On day 2, Josh Leavitt (of Ruta Locura and formerly of Titanium Goat) and I walked another student out and carried him back to town. We had to break camp, walked 8-9 miles to the TH, drive the student 2 hours to Billings, drive 2 hours back to the TH, and make it at least the same 8-9 miles back in so we could catch up to the rest of the group on day 3. Knowing the task ahead, we hung all of our food except a day's worth of snacks and anything else we wouldn't need in an emergency. I probably had 7-8 pounds in my pack and it carried fine. I also found it to carry fine the last few days with minimal food.
In hindsight though, I'd compress it down some before loading it so that the load is carried closer to the back with a taller but slimmer profile. I feel like this will get the load up near the top of the stays resulting in better transfer to the hip belt. Granted, with < 10 lbs transfer to the hips is not necessary for most men.
Does that help any?

