All things considered the GTX 660 Ti is extremely similar to the GTX 670. The base clock is the same, the boost clock is the same, the memory clock is the same, and even the number of shaders is the same. In fact there’s only a single significant difference between the GTX 670 and GTX 660 Ti: the GTX 660 Ti surrenders one of GK104’s four ROP/L2/Memory clusters, reducing it from a 32 ROP, 512KB L2, 4 memory channel part to a 24 ROP, 384KB L2, 3 memory channel part. With NVIDIA already binning chips for assignment to GTX 680 and GTX 670, this allows NVIDIA to further bin those GTX 670 parts without much additional effort. Though given the relatively small size of a ROP/L2/Memory cluster, it’s a bit surprising they have all that many chips that don’t meet GTX 670 standards.