There's no easy answer to your routing question. The Gulf Stream
is squeezed between FL and the Bahamas
and usually covers most of the gap between the two. Also accelerates.
One past the NW corner of the banks, about the latitude of Ft Pierce, the Stream widens, slows and moves a little further away from the US coast, leaving more room to go south down the US coast without bucking the current
If you try to cross the Stream and head
south on the east side you will be bucking the current unless you go so far east you are adding too much extra distance. However, if you try to angle SE towards Grand Bahama you will be longer in the Stream and bucking the current.
Best strategy is to cross the stream directly and spend less time getting pushed north. So go further south to cross you add distance but save time. One of the cases that the shortest line is not the fastest course.
If you have to go to the western Bahamas you just have to deal with the Gulf Stream.