Dirt 2 allowed for 2560x1600 gaming and, as you can see, there was no difference between 1GB and 2GB cards. As we said, only some games will actually report a performance difference between 1GB and 2GB versions of the GTX 560. You can check out the GPUZ shots below, which claim that Dirt2 is quite happy with 1GB memory buffers. On the other hand, Crysis 2 and Metro 2033 tend to like more memory, as they easily fill out 1.5GB of memory.
GTX 560 1024MB
GTX 560 2048MB