I have a couple suggestions that you might want to check out. I've been doing a lot of resaerch in this area for a trip to Glacier Park in which I'll be carrying a lot of shared gear with my girlfirend.
I selected the Nimbus Meridian for my trip, but my pack weight is about 34 lbs. I find this pack to be very comfortable with this weight, but I'm not sure how it would handle an additional 10 pounds.
I've also tried the ULA Catalyst which is very well constructed and I believe its specs say that it can handle 40 lbs. Personally I'm not able to get as good a fit (yet) with the Catalyst, but this is sure to vary from person to person.
Lastly, I think the Aether 60 might work really well for you. My brother has this pack and, if I were carrying more weight I'd have selected it. It's easy to dial in a great fit and, although it isn't ultralight strictly speaking, the fit and suspension are so great you wear the extra weight and don't really notice it. Plus, it's the only lightweight pack I know of that can handle 45+ lbs. without being overloaded.
Hope that helps.