You did the right thing talking to the Charter Masters. Good comment above about the 2005 season and the later October and November 10-day trips turning into cow hunts. I was fortunate to be on a boat during that 2005 bite and had a great time catching my first cow. But for me, the variety of a 10-day is more important than cow fishing. I'm quite sure I'm in the minority with that opinion, at least here on BD.
My vote would be an early October - and don't compromise away from a 10-day trip. Seems like a few 8-day Fall trips on boat schedules this year but the extra two days (or more if you want) give the crew so many more options if "Plan A" does not work!
Have a great trip - Fall is my favorite time to make a Long Range trip.