These are the official recommended power requirements for your GPU:
500 Watt or greater power supply with two 75W 6-pin PCI Express® power connectors recommended (600 Watt and four 6-pin connectors for ATI CrossFireX™ technology in dual mode)
This applies to the whole system not just your GPU.
The Corsair 650TX is a great PSU but doesn't have the four PCI-E connectors required for Crossfire on your graphics card. However the 650HX does have four connectors and is a modular PSU which will help keep your case clean and free from unused cables.http://www.newegg.com/Product/Product.aspx?Item=N82E16817139012