My 70oz camelback lasts me about 2hours. I fill it with cytomax and when it's hot I add a little dash of salt plus a dash of Morton's lite salt for extra electrolytes. I get leg cramps without the extra electrolytes.

I would have needed much more than you drank. I tend to sweat profusely though so it's possible I need more than average. My daughter drinks nowhere near the amount I do when we ride.

It definitely sounds like you were overheated...hydration and fueling may have played a part. Sounds like a break was the right things to do!