SYD-PER-MEL is definitely allowed (I have a ticket issued by AA with that routing, and they are strict with the allowed routing). All 3 cities are great rest stops (for different reasons, though personally I prefer CHC).
Thanks for the clarification on the 2 stopover/6 segment limit, I must have misunderstood the agent and didn't follow up as it didn't affect my tickets. The rules are complex to the point of being convoluted, though sometimes that leads to some favourable terms.