Couple of points having BTDT recently with LAX to SFO AA flights.
1. SFO airport is currently sorting out their runways which means the airport capacity is restricted in terms of take off and landings at certain times. In these times there can be quite bad delays as International/Long haul flights get priority. My LAX to SFO flight late afternoon flight was delayed by over an hour.
2. The train goes from the upper level and getting there takes a while - some of the signs can be confusing. Also when I was there last month one of the escalators from AA terminal to the train was not working. You can walk around inside the terminals if you want the exercise.
3. Security particularly fast track at SFO seems to move quickly.