Freddy, that was 14 months ago. Seven Hills' houses are selling around $750k mark.
600k house - Mt Druitt / Penrith region perhaps. Though not sure if there is much value in buying those now.
It seems as though the market is at peak.
Not quite true MsAli- you can certainly still buy houses in Seven Hills, Lalor Park Blacktown LGA (don't forget Kings Park side) for the $600K's though most now are starting from mid $600K's rather than low. Renovators delights, crappier main rd/DOH stock streets positions etc. They're still out there though getting much more challenging to find.
OP- I can't comment on GP or Glenfield (not my areas of knowledge) but would also urge you to consider townhouses/villas if you want to retain some land value and can live without a house. Lots of other suburbs to consider- Sydney is a large city after all