program on m2070

I troubled when I program on c1060 ,I need use more than 4G global memory on gpu, so I buy m2070,it should has 6G global memory.I use the sdk sample deviceQuery,it shows that it only has 4G global memory,and when I copy data to the memory ,it more slowly than c1060,what should it be?can any one help me,I use the newest driver NVIDIA-Linux-x86_64-270.41.06,and 3.1 sdk.thanks a lot