We've done the Oz-NCal trip around a dozen times. We've left from as far south as Sydney
and as far north as Mooloolaba. We've come to the conclusion that the optimum place for u s is Southport. We too wait for a low off the NSW coast, and anticipate one to three days of W'ly quadrant winds. We sail ~due East until headed, and then follow the gradual backing to the SE. Usually end up with a nice close reach into Passe Boulari.
However., we most often go in August or September, not May. That's still winter, and the frontal systems that sweep across the Coral Sea
are a bit more intense, and the air and water
are colder and not to our taste. And in general, the farther south you start out, the stronger any frontal system will be as it overtakes you.
However you decide to travel, enjoy your passage
. NC has become one of our all time favourite destinations, and is usually an easy passage
if you are patient!