British Expats - Advance shipping

We will be emigrating to Australia in December. We are flying Emirates, and though their luggage allowance at 30Kg is more generous than most other airlines, they do not offer any increase for migrants, and have a very high excess luggage rate.
The container with our belongings won't clear customs before mid January, so we are considering sending some of our clothes and shoes in advance, possibly about 15/20Kg. If we send now, it does not even have to go necessarily by air.
Anyone else done this? Any suggestion of carrier and prices would be appreciated.