Certainly ambitious...............You did not mention the boat You are chartering or your crew. Both could influence your performance potential.
Of course, the weather & wind direction would have to cooperate too.
Have you thought about doing a one-way charter which would allow you to cover same (or even more) distance but slow down enough to smell the flowers or taste the rum?
Also factor in the waves / open water between islands which depending on your course & wind direction could add speed or create a bashing day
P.S. Definitely check out Grand Case (NW corner of SXM) for atmosphere & eating.......as you zip by