you'll probably save a few miles by going I-75 to the turnpike and catching up with I-95 near Fort Pierce.

While I-75 can have backups, so can I-95. I have never had bad traffic on I-75 (I take it from Detroit to the Tampa area all the time), although they did close a stretch of it a week or so ago due to smoke from fires.

You may be aware that I-75 does not go to West Palm.