Jim, I know this is obvious, but since both options could work, I would talk to your captain to get his or her perspective. Personally, we love St. John, but since you have a limited number of days, I would want to clear customs on your travel day to get it over with. Of course, you can do this either by taking the ferry or having your captain pick you up. A key factor will be your itinerary. If you plan to start the trip in the Jost or western side of Tortola area, taking your boat may make more sense. However, if you plan to be in Virgin Gorda the next day, taking the 5:00 pm fast ferry to Road Town would avoid a big chunk of this long journey at 6 to 10 knots.

For our family, we try to avoid the ferry. Therefore, we would probably start our trip in the Sopers or Jost area and pick up the boat in Red Hook.

Good luck!
Steve