Quick question about the GTX 670

So I'm bulding a rig with this card however I've noticed a massive difference in the prices of various versions. Can somebody please explain the difference between the linked cards? I know it's something to do with overclocking and the more expensive ones seem to have higher clock speeds, is it worth getting one of the more expensive ones?

$484
http://www.cplonline.com.au/online-shop?page=shop.product_details&flypage=flypage_default.tpl&product_id=10664&category_id=341&keyword=gtx+670

$509
http://www.cplonline.com.au/online-shop/graphics-cards?page=shop.product_details&flypage=flypage_default.tpl&product_id=10670&category_id=264&keyword=gtx+670

$529
http://www.cplonline.com.au/online-shop?page=shop.product_details&flypage=flypage_default.tpl&product_id=10658&category_id=341&keyword=gtx+670

$579
http://www.cplonline.com.au/online-shop?page=shop.product_details&flypage=flypage_default.tpl&product_id=10659&category_id=341&keyword=gtx+670

The more expensive ones offer varying degrees of Factory Overclocks, something you can easily do on your own but might void the warranty of a non-factory overclocked card.General_X

[QUOTE="General_X"]The more expensive ones offer varying degrees of Factory Overclocks, something you can easily do on your own but might void the warranty of a non-factory overclocked card.JC_Spot

Looking at various benchmarks, the most expensive ASUS one outperforms a stock 680.JC_Spot

[QUOTE="JC_Spot"]Looking at various benchmarks, the most expensive ASUS one outperforms a stock 680.General_X

[QUOTE="General_X"][QUOTE="JC_Spot"]Looking at various benchmarks, the most expensive ASUS one outperforms a stock 680.JC_Spot

I have the Gigabyte Windforce 670 I got off newegg for $400. In precision x I can clock it to 1180 and with boost in heavier games in battlefield 3 I see it hit 1324. The card is the best price performance card on the market atm and I highly recomend it. My temps never go above 62c ever.