I am looking at picking out panniers for a summer tour, and I am trying to decide between 36L and 43L. I will also have about 7 L of space for small items between a seat bag and handle bar bag, plus 2 cages for water. I definitely prefer the light side. I don't mind trading comfort for space.
A rough idea of things I plan on taking are: Hennessy Hammock, Trangia stove, summer sleeping bag, small air mattress, small bike pump, some tools, spare tire, spare tube, change of cloths, rain gear, flip flops, food, fuel, first aid kit... and probably a few things I am forgetting right now.