Upgrading graphics card

I have a gaming pc and I want to upgrade the graphics card to get better fps, what would you recommend I upgrade to. I have a budget f around €200 - €300

 

 

CPU: Amd athlon 750k 4.0GHz Quad coe

Ram: 8gb  1333Mhz DDR3 

Graphics: Amd radeon 640 2gb graphics card

Motherboard: Gigabyte FM-2  GA-F2A55M-DS2

Power supply: 430W Basic PSU

OS: Windows 8.1 

R9 270x would be my choice.