I'm planning a tour from Denver to Philadelphia starting in April, and am trying to scope out some new water bottles/cages. Last summer, touring from Portland, Oregon to Walden, Colorado, I used two store-brand 21 oz bottles (stored in the cages) with another two 25 ounce insulated Polar Bottles (kept in the panniers.) but it was not nearly enough. This year's tour will doubtless be less water-scarce, but I'd still like to scope out some bigger bottles, and perhaps mount a third cage beneath the frame. The problem is, the cages that I've been using (cheap Planet Bike jobbies) don't provide enough support for the 24oz bottles, and will most definately not be sufficient for the 28oz bottles I just ordered online.
(On a side note, the water in my Polar bottles tended to turn sour after more than twelve hours, which never happened with the clear 21ouncers. Just a friendly observation...)