Ok to add to the above, it's a family break with the kids, not a business trip.
We would be connecting through to Sydney. Frankly I'd rather transit in HK than LA or Dallas, and the CX price is good, hence looking at the CX option.
We have OWE status - is there a decent lounge in BOS that CX pax can access?
I think I can just about make it work with a late checkout and a longish loiter in the lounge (if available), as long as I can get the luggage checked in at a reasonable hour.