number_6, thanks for your insight. I do worry about being stranded in the mountains but likely wouldn't complain if it happened. Our schedule isn't going to be so definitive, other than getting to Sydney on the 25th for the wedding.

I've been told by others that it is not recommended to drive to Milford Sound during the winter? Black ice, road closures, etc...seems a lot of locals recommend going with a coach/tour to be safe. So your suggestion to drive ourselves confuses me

Thanks again for the help. We may just drive to/near Chch and try a day trip to Mt Cook if the weather allows.