The main advantage of the 757-300 is that their are 50% more available for your unlikely upgrade making it somewhat less unlikely.

The 8:00am SFO-EWR flight is typically a 757-200 with International Business-First seating although regular transcon service. It's very unlikely that you will upgrade on this flight (16 FC seats) but it you can do a B or Y-up, it's a treat. Also has AVOD in all seats.