I'll add my 2 cents to the discussion.
Zero needs to clarify their naming conventions. As far as I can tell it is like this: S (Street), SR (Street Racing), FX (Super Moto), FXS (Stealthy Super Moto), DS (Dual Sport), DSR (Dual Sport Racing), FX (Motocross). SR/F (Street Racing/Moto??) SR/S (Street Racing/Stealth).
I am going to guess SR/S is a lighter, cheaper, SR/F, possibly with a smaller battery pack. But I'm probably wrong.
As for fairing. Zero does not have to spend much to design a fairing. They are not in racing, so it does not have to have maximum efficiency.
Most of their design features are off-the-shelf. In any business it is common to have the OEM manufacturer design new stuff, like a motor, or new shape battery-pack, against a contract to purchase certain amount of items.
AC or DC charging are very similar, neither has a clear advantage just by being AC or DC. There are other factors in play.