I have experimented with putting Heed in my 50 oz Camelbak for my rides that are 3.5 hours or longer, taking two water bottles of Accelerade, and powder for both in my seat post bag just in case I need to replenish along the way. That 100 ounces seems to be working for rides of up to 4.5 hours. I suspect that I am still not drinking quite enough, however I feel fine and haven't had any problems with thirst. Of course it matters how hot it is and how many hills there are - hills require more effort AND I find that I drink less in the hills.
The Camelbak doesn't seem to be holding the flavor of the Heed, but I clean it very, very well after the ride. I like the new strawberry flavor.
I still need to get those scales and weigh myself to make sure I am drinking enough...