Which speed are you referring to.? If you are referring to final rendering, then it totally depends on the CPU.. If you are referring to desktop rendering then it depends on the video card.. It looks like you are on a crossfire setup which is no way beneficial even with the 4 GB frame buffer that it offers.. If this build is purely for professional use than i'd recommend you to use a single video card.. For further suggestions and advices, it'd help if you could mention the software you are using..