Positioning flights
I am sure many of us now need to figure out how to get to/from ORD. In my case from NYC... preferably LGA or HPN. As I look into this there are a few things folks need to be aware of. First, if you are on NZ metal from ORD you are going to depart from T5 which means that you need to factor in enough time to transfer from the domestic arrival terminals over to T5.
Second, don't assume you can stay airside... you may have to collect your checked bags in ORD and take them over to T5 yourself. Be sure to check the interline agreements to see if you can check bags from your originating airport. E.g. AA explicitly will not interline and through check your bags onto NZ. UA might as it seams they will for *A even if separate tickets/PNRs. So be sure to allow lots of time in ORD on the outbound (I am going to plan around 3 hours minimum but 4 might be a safer buffer... depends on time of year too in case of weather, I am October so should be okay on that front).
On the return journey interline is less of a problem as we have to collect our bags to clear customs anyway. I assume that the major airlines (UA/AA/DL/etc) have baggage check-in at ORD T5 for arriving passengers... and can print baggage tags, not just accept bags that are already tagged to final destination.
Finally... there is always a risk with not checking bags to final destination. If for some reason you bags do not make it to ORD on your positioning flight then you have a huge problem. I assume there is no obligation on part of the originating airline to get the bags to you in Aus/NZ. In other words, having typed all this, I feel like carry-on is by far the best option just to be safe.
DAK