Direct answer: The major difference is how the gate is manually released during a power failure. FR uses a foot-release pedal, FSC is fail-secure and uses a crank, and FSF is fail-safe and can be pushed open when power is off.
What stays the same
Eagle publishes the same 27-foot / 600-pound maximum for the 1000 FR, FSC, and FSF family and rates them for continuous duty. Choose the release behavior based on how you want the gate to behave during an outage.