Starship payload to LEO is about 100 tons
Falcon 9 second stage needs about 100 tons of propellant.
If a Falcon 9 second stage waits in orbit, a Starship comes and refuels it, then Falcon 9 uses all that fuel towards Pluto then how fast the Falcon 9 or its payload can get? Can it get faster than New Horizons 16 km/s ?
More or less of course.