Neither are good my recommendation:
PCPartPicker part list /
Price breakdown by merchant /
Benchmarks
Power Supply: XFX 650W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply ($79.99 @ NCIX US)
Total: $79.99
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-09-28 19:49 EDT-0400)
The brand is what matters, 650 watts is more then enough to crossfire those two cards. CX series from Corsair aren't the best built, even tho XFX, Seasonic and Corsair are the three top brands for PSU's. Hope this helps and please remember to select the best solution so that others may learn from this thread. Thank you for your time.