What needs the extra ten liters?
Identify what would not fit comfortably in the smaller option and where it would go here. A bulky layer is a different packing challenge from a rigid lunch container. Inspect the opening and pocket shapes so the additional volume translates into useful space for those objects instead of just a bigger exterior.
GO 25L after the trip
If this will also serve as a local daypack, think about the lighter load you carry at home. Check its empty dimensions and how the organization works without travel clothing inside. Review the specific security instructions and keep the operating routine simple enough that the advertised features remain useful in ordinary daily use.
