I don't know much about RM Williams, so can't comment.
Michael, what do you mean by a 'great' sport coat? Some people might prefer a stronger shoulder, others want one with softer shoulders, some want patch pockets and others want something else entirely. And, then there's a question of budget.
Navy, soft shouldered, light buttons, patch pockets. Preferably less than $400.
Even the beige is quite nice - except it doesn't have patch pockets.