With the small difference there, you won't see any difference between the cards unless you run a benchmark on them. A rule of thumb is that a video card, or a computer in general, has to be 20-30% faster before you can really tell the difference without a benchmark. You're looking at a few % difference in speeds. Get whichever card has the best warranty and/or price and reviews.
Will the higher core clock or the higher memory clock show a bigger difference? I will not be overclocking it and I have PCI 3.0 on my mobo.
Although you cannot compare cards like this to figure out which one is "better", all things being equal, core speed relates much closer to a difference you can actually see than the memory clock. As rule of thumb for instance when overclocking a GPU, you always work with core speed first to attain the best performance possible, then tweak the memory speed last to gain that miniscule fraction of a percent more. It may even be beneficial in your overclocking efforts to lower the memory speed if it will allow you a higher core clock and end up with better performance.