Which 7970 is the best?

I've heard that the 7970 can destroy the 680, and i was wondering which 7970 will give me by far the best performance. Price doesn't matter. I'll pay upwards of 600 for a good card. 

http://www.newegg.com/Product/Product.aspx?Item=N82E16814161412

I have two of these running 1150 core 1700 memory on stock volts and can't make them overheat.