In 2000, WA's per capita income was about the same as in Queensland or South Australia but lower than in either NSW or Victoria. But WA has seen easily the largest increase over the intervening period. Today WA enjoys the highest per capita income of any state, at around $ 000 per person per year.
It is true that the ACT and NT boast higher figures, but they are very unusual cases, being heavily influenced by the effects of government employment and/or subsidies, not to mention being quite small. It would take quite a few years at the current pace of growth for the other states to catch up to WA.