Okay, I suppose that the corsair one will do. And will I be needing to purchase extra cables?
Nope the Corsair includes the required pci-e 6pins required to power 2x6850's.
2X6870 = requires 4xPCI-E 6pins the Corsair TXV2 only supplies 2 = although your cards includes the molex adapters = would be fine.
Psu that includes all necessary 6 pins without the need for adapters.
XFX Core Edition PRO650W = supplied with 2 x 6-Pin, 2 x 6+2-Pin http://www.newegg.com/Product/Product.aspx?Item=N82E168...