Doesn't make a great deal of difference as the outstanding mortgage on your investment property (your current home) will be fully tax deductible. It is your home, your money so if you choose to re-mortgage and use it as an income producing asset then you can claim the lot.
One question however, if your current home is worth $400k as valued by the bank, then why don't you re-mortgage to the limit ($360k) and use that money to minimise the debt on your new home? Interest on your new home is not tax deductible so use the investment property for it to be.
