I am the squad leader of a scenario paintball team. We carry 30 pounds of equipment on long shirts/pants in Texas summers through 24 hour long straight games of paintball over very rough terrain.
We all use 2 liter camelbaks and have been extremely pleased with them. We go through about .75L-1L an hour. Size, weight, and flexibility where huge parts in our requirements and the camelbak meets all our requirements.