From what I have read of the research, more definitely isn't better, and I think it can start to be detrimental after about 5 cups per day.

The break is necessary for resetting the adenosine receptors in our brain. Adenosine is the neurotransmitter that makes us feel sleepy, and caffeine blocks the receptors, meaning adenosine can't bind and we therefore don't feel sleepy. But our brains will just keep making more receptors to compensate, meaning you need more and more coffee to get the same effect. Similarly, when the caffeine is metabolized over the course of the day, you're going to have a bigger crash, as suddenly a bunch of receptors are open.