The download is slightly slower, but the upload is significantly faster.
Standard Cable is 30/1, Standard NBN on Telstra is 25/5,
So you lose 5Mbps of Download but your Upload becomes 5x faster.
It is a bit of give and take.
That being said, if you went to ADSL, you would pay the same and only get upto a maximum of 20Mbps.
ADSL, NBN, Velocity and Cable are all considered equivalnent services and are priced the same, the speeds obtained are limited to the technolgoy.