For a system using a single Radeon HD 6850 graphics card AMD specifies a minimum of a 500 Watt or greater power supply. The power supply should also have a combined +12 Volt continuous current rating of 24 Amps or greater and have at least one 6-pin PCI Express supplementary power connector.
The OCZ ZS Series 550W (OCZ-ZS550W), with its +12 Volt continuous current rating of 38 Amps and with its one 6-pin and one (6+2)-pin PCI Express supplementary power connectors, is more than sufficient to power your system configuration.
Sorry for late reply, anyways thanks! It'll put me to about $770, but it's worth it and there's $75 worth in MIR.