The availability of top grade commercial office in Sydney is in...

The availability of top grade commercial office in Sydney is in fairly high demand at present Pete, hence the reason the big builders (Lend Lease, Multiplex, etc) are so eager to get major projects off the ground in Sydney at present. I can't speak for the other major cities I'm afraid. There are some huge developments on the cards around Circular Quay over the coming years, as well as a number of other areas. This page gives a bit more insight on this FYI: http://www.smh.com.au/interactive/2016/sydney2026/chapter6.html

I wouldn't have thought that the residential market going cold would hit the commercial market too hard in the first instance. If a resi market drop triggers a recession this would be sure to have knock on effects on office space too, as companies start to downscale operations to ride things through.

Purely speculation on my part, but that's my take on things as they stand.