Option 3 is definitely the best option in this case.
1st you save a few thousands on mortgage insurance. (2k or so)
2nd The interest you earn form bank deposit is less than the interest cost (6.0% vs 7.5%)
Not to mention that 7.5% in ‘gross-up’ term is equal to 10.7% (assuming your personal margin tax rate is 30%). that is, you need to earn 10.7% (before tax) or more to be better-off than reduce your home loan.
In Australia, tax is big consideration in all your investment.