DL runs sales to SYD. I have never done a Chinese airline long-haul in coach for a reason - I have heard it is not comparable to DL.
DL runs a plane with almost half of Main Cabin as Comfort + seats on this route, so you will have a comfortable ride all the way. Maybe even a decent PS offer.
I would wait for a DL sale. I have seen NYC or BOS to SYD for as low as $550 on DL roundtrip in coach (during a fare sale).