A warp of 32 threads takes 4 clock cycles to propagate through the shaders, so the core clock (which controls the instruction decoder) does not need to be as fast. You can't control the core clock and the shader clock separately, so their exact ratio is set by some internal hardware requirements that people outside NVIDIA aren't privy to. For performance estimates, I don't think you need to pay attention to the core clock at all.
Halp warp of the 32 threads takes 2 clock cycles.