I've had many opportunities to test these roads and this (below) is the shortest mapped route I can find. It may not be the fastest, in which case I have a different route that avoids many high traffic zones. This route includes some unsealed sections.
Notes: If you want to get a wriggle on, best to cross the Murray at Nyah rather than use the B12 which is often patrolled. Continue thru Chinkapook and join the A79 before continuing into Ouyen. Adds about 8kms but you'll enjoy the very light traffic. Road is narrow in places, so use caution with oncoming traffic.
Some sights from along the way: