What is the difference between all these R9-290s? One is $519, $639, and $662? Is one better than the other?
There can be many differences. Quality of the components used is a big one. Cooling is another. Usually the GPU manufacture (Nvidia and AMD) will design a card and use it as a reference design. The card manufactures can use that design or make their own (some do both) and use custom PCBs and coolers for the card allowing for better cooling and overclocking.