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You can't overclock an 9500 into a 9700, there are differences that must be overcome on a software level that can turn some 9500s (nonpro only) into 9700s, but it's really not overclocking.
The cards you're looking for are the ones that have their RAM chips laid out in sort of an 'L' pattern around the GPU, as opposed to the ones that are all set in a straight line. You should be warned though, that even having a proper card doesn't guarantee a successful mod.