I ended up deciding on a GoLite Pinnacle in this situation. It can handle anything from 25-70+ liters. The only issue I had was when you got above 25lbs total, the supplied foam backpad would buckle just above the hipbelt. Still carried OK - was just an annoyance. I had up to 32 lbs in it. I've since removed it and just use a foam pad as a burrito for the structure. I've been very pleased with it.