One thing I'm wondering is what your wife's torso measures... in other words, at 5'6" she might measure for a medium frame, in which case she could wear your medium Jam, and you could get the "load monster" Ohm or something. Or if you haven't used your pack yet, return it? The reason I'm sticking to this line of thought is that those times you're carrying 35-40 pounds you'll be at about double the weight I've found a Jam to be comfortable. Double the weight! Why suffer?
(And yes, I do carry the heavy pack in these situations, and I do understand why you'd rather be the one suffering, but personally would rather carry the extra weight comfortably so I can enjoy the trip as much as possible as well.)
David, not to stick my nose in, but a fellow BPL'er was good enough to bring an Ohm and a Catalyst into the shop for me to try on. I think we had them loaded with about 25 pounds, plus pack weight and a little stuffing. I also tried the Jam again at that time. Discounting all other experiences, even at just 25-30 pounds I found the Ohm worlds more comfortable than the Jam... and I do own a Pinnacle, so I'm a little biased toward the GoLite.