Cash fares to/from PER from the east coast can be expensive. Awards can be good value. A ~6:00 hr flight. NZ is closer (and cheaper) at 3:30hrs
I would not go to WA for 4-5 nights (travel time)
PER will be a hot as ADL. The hot winds blow from WA to SA
http://www.gcmap.com/mapui?P=c%3Ablu...=bm&PW=3&DU=mi

Edit
Look at the climate data at the bottom of the page
https://en.wikipedia.org/wiki/Perth