It seems unusual that you would be told those speeds. Nbnco.com.au offer 25, 50 and 100mbps services as their standard products. There is also 12mbps which is considered their basic offering. (source
Choosing the right speed on the nbn? network | nbn - Australia's new broadband network) Some retailers may offer alternatives but generally they stick to the vendor rated speeds as it allows customers to compare apples with apples.
You should probably seek alternative advice regarding the speeds quoted. Also the speeds delivered via the copper based vdsl are generally worse than the quoted service speeds.