Most people use the 4-pin psu to 6-pin pci-e adapter.
Your power supply has enough amps.
I don't see any problems.
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)
Certified power supplies are recommended. Refer to http://ati.amd.com/certifiedPSU
for a list of Certified products
This should be fine:http://www.ebuyer.com/product/132563