Mind you, 1500 lots coming on line in the next year or two will have an effect.
Just don't know by how much.
My guess is maybe up to a 20% dip or no change in all. Just don't see prices increasing for some time to come after the two year land release period.
Same goes for Port Hedland. Looking at population forecasts they a predicting a 10% dip around 2015 as some of the projects are completed and switch to an operational work force.
BUT, both Karratha and Port Hedland are being planned as 50,000 people regional cities, so there will always be demand keeping a floor for property prices and rents.