wasabi2k: Banks will usually make the break fees prohibitive enough to not bother, but worth a try.
This is not true in my experience (with ASB). Their break fees (Early Repayment Adjustment) are essentially equal to the PV of the difference in interest payments between what you agreed to pay and what their current rates for the remaining term. You can't get any fairer than that.
You win if the shorter term rates are higher than the rate you fixed at (i.e. no ERA probably). You could also win based on any number of other interest rate movements.
Although I note that for loans documented on or after the 1st April 2015 they calculate it with respect to wholesale interest rates, so things might have changed there.