I'm a retailer & packfitter, and spend a lot of time fitting these packs and many others.
The Exos and Aura frames are different, but they are similar in the design issue you had trouble with. Both have that radius down low. I have had a few women fit an Exos better than an Aura, but not often. The shoulder straps have much less curve, & I don't think your concerns would be fixed.
The Ariel is a great pack, industry-leading seller... because it fits a ton of people really well. There's only a ~1oz weight difference between volumes. A small would probably fit you quite well w/fit dialed in. The custom hipbelt molding isn't necessary for a good fit, just helps reduce "break in" time. The Ariel frame is distinctly different than the other two we've mentioned, and I think it'll work for you. No point going to the Xenon frame (or the XS, if you're @16.5" torso) unless you're planning for some monster loads.
Other more widely available models that you might try for comparison would be the Golite Wm's Quest in medium (same as normal small), Gregory Jade 60 small, or Granite Gear Nimbus Meridian Ki. Might also try a Deuter, such as the ACT Zero 55+10SL... pretty light for its size.
I suspect that a properly-fitted Ariel 65 would make you pretty happy. If you might even push that 50# max, the Ariel would likely carry it best out of the packs above... but it all comes down to fit. Since you already have the line open w/Osprey, I'd go for the Ariel and take it from there. FWIW, if it fits I'm pretty sure you could cut into it and remove nearly a pound of extra weight... if you're comfortable taking razor, needle & thread to the new pack.