Here is a suggestion, The xfx 280 is factory oc'ed and a good price, the PSU you have now only has 1 6pin pcie connector and is of really low quality so you will need to replace it as well to run the 280.
PCPartPicker part list: http://pcpartpicker.com/p/n3WpmG
Price breakdown by merchant: http://pcpartpicker.com/p/n3WpmG/by_merchant/
Video Card: XFX Radeon R9 280 3GB Black Edition Double Dissipation Video Card ($159.99 @ Newegg)
Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply ($44.99 @ NCIX US)
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-04-21 06:31 EDT-0400