By your name I am wondering if you are an Aussie. If so a lot of the medications that are being moted on this Board are not available here at home.
We have crossed the Tasman and we did not strike it to be rough and that
was in August, our winter. I know this year that the seas were very bad in January. One particularly crossing by the Statendam at the end of January was horrific. You can never tell if you are going to have a smooth or a rough crossing, it does depend on the weather patterns and it is just luck.
If you are prone to seasickness, go and get some good medication and start taking it before you leave Milford Sound so that you body has absorbed it and that will help you with the motion.
We were on the Pacific Princess in January, going to Vanuatu from Sydney and we had 3 days of Force 5 seas, which are not huge, but enough on that smaller ship to make a lot of people sick. On the bigger Statendam, it would take bigger seas to affect you.
Until we sail on the Tahitan Princess - Tahiti to Hawaii
Until we sail on the Nautica - HongKong to Athens