I have the HPL20 as well. Great pack, generally very comfortable, even with no shirt under it.
I'm going in Art's direction now...2 24oz. handhelds with the Nathan for food and clothing. I find I have a hard time gauging my hydration rate/remaining water supply when it's in a bladder on my back. With handhelds I have an easier time rationing my water.
For a R2R2R I'll likely carry the two 24oz. bottles, possibly with one extra in the pack (depending on our sources).