Thanks, all you gals; this is very interesting.
Frito, my radically female significant other needed an AT pack and had not been able to find anything she liked, so I made this pack for her:
* Frameless, straight-through bag padded by the sleeping pad, and made short to stop at the small of the back, not on the butt, and contoured to fit back;
* No hip belt at all;
* Wide, cobra-style shoulder straps (wide on shoulder tops, narrow in front, countoured radically to keep them off the mammaries;
* Load-lifters on top of the straps at 45 degree angle.
It is good to about 30 pounds (and has gone, less well, to 35), but she very rarely carries more than 26 total.
I agree with the comments that a pack that bangs your butt is at least obnoxious if not actually painful – for men as well as women. I have failed to design an adequate hip-suspended system without adding a lot of hardware (and weight). However, eliminating the belt entirely and stopping the pack before the sacral promontory starts works very well. Carrying it all on her shoulders seems to work ok for Frito despite a lot of rotator cuff surgery.
And Ron,
There is another reason to put the shoulder strap top anchors closer together for women: It changes the angle at which the straps ride on the shoulders and gives more uniform pressure across the width of the strap for most women. However, this causes the strap to turn toward the (can't refer to them puppies here), so a radical contour is needed to turn it to the outside. Doing both and widening the strap on top of the shoulders seems to work fine for Frito. Combined with properly angled lifters, properly designed shoulder straps do not need sternum straps at all. In fact, IMHO, sternum straps are evidence of poor design. But maybe that's just me. Personal prejudice: done right, a pack should be stable for nearly horizontal climbing without a hip belt, much less a sternum strap.
Spock