dilemma88, I'd suggest you take up a 3 year degree first for the following reasons:

1. Many people change their courses half way through their studies because they have been disillusioned/lost their passion. If you think law is for you, go ahead.

2. You would gain an additional 2 years of working experience if you studied 3 years instead of 5. I did my undergrad and masters (5 years in total) and found that much of what you have learnt at school is pretty much 'useless'. I learned a whole lot more in the first 6 months of my job than at my first 3 years at uni.

3. Financial implications - Don't forget about opportunity costs. You would be losing about $80,000k in income (assuming you hold a normal job) over 2 years + an additional 2 years worth of intl student debt.

4. As for banking, are you refering to investment banking? If so, what matters most, at analyst level, is your GPA + school name + networking. Unfortunately, I don't think UNSW quite makes the cut in terms of elite schools if you are looking to work at Goldman/JPM/Morgan Stanley. But its still definetely doable if you manage to score > 6.75/7.0 HDs in your undergrad.