I have not done this through SFO. Have you checked the on-time performance of the incoming flight (ie, the reliability of the arrival into SFO)?
Say you are 30 minutes late into SFO, then that may be a problem. What if it took you up to 60 minutes for baggage and immigration, then bag drop and then transfer to another terminal. How would that affect your stress levels?
Edit: For example, looking at UA870 SYD-SFO, Expert Flyer shows it as having an average delay of 35 minutes over the past 2 months. Also, welcome to AFF.