Well im not exactly sure what your trying to ask. But your memory clock is usually around the same as core, but you double it for some reason(idk). SOmeone else could better explain it.
like all overclocking it is done in baby steps with trial and error (baby steps to minimise the error ). the core speed is what makes the most difference so concentrate on finding the maximum that can be taken to and kept stable. then take the core back to stock and repeat the trial and error with the memory. finally get the best combination of memory and core clock.