DDR and SD RAM are synchronous devices (as opposed to eg. compact flash storage). Their performance is entirely given by clock frequency and timing parameters. Hence running the RAM with the same clockfrequency and timing will give you identical results.
However, the RAM module has a small eprom onboard that holds the timing information (this is also referred to as the SPD). A good quality module may have faster timing settings than another, and hence running them out of the box without overclocking may result in marginal performance differences.