Buy into a Perth office deveopment vs industrial factory unit

I am in a bit of a quandry which way to go , I already have  2x houses and one factory unit leased out . An opportunity  has arisen for another factory unit well priced in Malaga (Perth ) when calculated for rental return it is about 6% But which doesn't factor in Iwill initially have to pay GST because it is vacant possession.
$379000.+gst .I would have to pay 40% to keep repayments down on a loan to make it work.

The office in  the cbd gives 8% , (these are net  but before personal tax of course ),
The offices have one  carpark bay each that goes with the purchase which in itself is a 9% return .It is a30 year old building completely refurbished to 2010-2011 year standards ,I have had a look in ,each floor has been subdivided with titles and sold off individually, the developer/agent splits up the rent as some tenants have a whole floor leased .And so now separate landlords for various sections .

There are other office buildings towers etc projects going up in Perth cbd .It is said to be cashflow positive , and have potential future growth  , With a tenant already in place ,so no GST .
Approx $465000.for the cheapest ones left the rest are over this amount .

I have about $ 230000 ,cash to spend , or  keep .
I still owe about $115000 on one house .

Any opinions appreciated .Thanks .