That's one of the many advantages of dealing with a well informed mortgage broker. They know and have access to the serviceability models of the various banks. It's not all about living expenses, either.
For example, some lenders are using an assesment rate of 8.5% at the moment (ING for example), whereas others are using P&I repayments to assess serviceability, even though you are applying for an IO loan.
Also, there is variation depending on personal circumstances, too. FOr example, one bank might have a great serviceability model for singles, yet a poor model for couples with dependants, so depending on your circumstances, you really do have to explore he options and not just rely one someone telling you that bank X has "the best" serviceability model.
According to the bank person that I randomly popped into the other day, they've put up the base living expenses. She said something like if you say you live on $1000 a month (which we do, and she said she does too) they won't believe you and just put down $2000.
Wonder how I explain that mysterious $1000 a month that I save (ok, not save, I give my surveyor ... plumber ... council) then? That is sooooo not living expenses, unless it is a regular occurrance to subdivide.
Pretty sure they all have different formula's for this. Personally I have found it to be quite frustrating as our living expenses tend to be much less, and we have a salary sacficed car, which means all our car related expenses come out in pre-tax $ - But many still insist on leaving a 'car' expense in the equation anyay, which means we are theoretically paying for the car and all related expenses twice.