You'll probably want as little weight on your body as possible, for reasons of saddle and back comfort. If you use one of the XLab (or similar) brand gizmos that allow you to put two additional water bottles behind the seat, then use Zefal Magnum water bottles which hold 32 ounces each, you'll get 128 ounces with nothing on your back, and none of the Camelbak-cleaning problems. I use four of these bottles, two on the frame in the normal places and two more up high behind my seat, above the huge seat bag.
Edit, based on following posts: Four of the 32-ounce Zefal Magnum bottles (two going behind the seat) holds a lot more than any Camelbak! Four of the largest of other brands of bottles (28 oz each instead of 32) still comes out to 112 oz which is still more than any Camelbak.