In case anyone found that study difficult to read, the optimal strategy was, over the course of 3 days, one 600mg dose after 12pm on days 2 and 3 of a 3 day string of sleep loss.
In my own case I've been tracking caffeine use and some helpful strategies are:
- 30mg after a brief afternoon nap
- 50mg to 60mg after a long afternoon nap that resulted in grogginess
- 100mg after a terrible night's sleep and before a long meeting
- Extreme care if I have an exhaustion headache due to lack of sleep and overproduction; caffeine often triggers migraine here
Table 2 suggests that to match the performance of studies 3 and 4 (done by other researchers), which each gave 600 mg of caffeine, they were able to cut the dosage down to 500 mg and 400 mg respectively. But it's not clear to me that they're recommending that as the overall optimum, and that's the only place I'm finding "600" in the paper.
Sadly, my sleeping problems don't have clear external factors like that so I usually don't know if I'm going to have three days of bad sleep ahead of time like that.