For those who are curious we arrived at SFO at around 4:45am for a 7:30am departure. There were at least 5 counters open and no lines. Next time I would sleep in another hour and arrive 2 hours before departure. (Also no security lines at that hour.) We could see the plane sitting there from the night before and they did not even fire it up or attach the jetway until about 1 hour before departure. Turned out to be a full flight.

I will report back from CUN in a week - last time we saw 3 hour lines for most US-based carriers but I'm told MX has the best operation here.