I am going to get a hydration pak, and am curious about what size people recommend. It seems to me that the 100 oz bladders would add significant weight. I was thinking to get a 50 oz size - which should be good for a couple of hours, and I have take another bottle on the bike frame. However, someone suggested either a 70 or 100 oz. I could fill them less than full for shorter rides, but for the 3 centuries and one double century I plan to ride this summer, I'm wondering if I don't need the larger one.

I would be happy for the any suggestions from those more experienced.