The prices are defiantly not the same, it should be cheaper, but it isnt I am from Aus, the i7 2600k cost about $329 or so and every 580 is over at $550 it is kinda stupid with exchange rates and stuff
GTX 500 series I would say because it will sitll be able to play all new games that come out for the next 2 years or so, which will give you more then enough time to gather more money for a minor upgrade here and there
Whether you should hold out for the 600 series next year really depends on how good your current system is. The new 600 series will be very expensive when first released, and driver support may be troublesome initially. However the performance gains of the new cards should be much better while using less power.
Just be warned, you will be waiting about 6 months until the GTX 600 series are widely available, and until the drivers are working well. If you cannot wait this long then I'd recommend getting the GTX 570 as you have planned.