Personally, I would still use the route through Nagua, and Google Maps agrees with me that it is quicker from Cabarete. I do the trip to San Pedro de Macoris quite often and have always found this route best.
I was talking to a Dominican architect the other day, and he is working on the new Autopista which is due to go from Puerto Plata area to Santiago. It sounds like a hell of a project, with no turn-offs - just a direct run from the north coast to the Santiago by-pass, going through two tunnels. He says it will be done in 2-3 years. Now when that's done, the route via Santiago may be better.