I tracked my productivity pretty rigorously in college for about a year. My maximum sustainable productivity was somewhere between 6 and 8 pomodoros a day. If a deadline was imminent, I could "crunch" and put in something like 12 a day for a week. Interestingly, I would crash afterwards and can only do about 3 pomodoros-per-day until my brain recovers. The average productivity in the crash + recovery cycle was also 6! So I was just borrowing from future productivity.