There was a period of time a few years ago when memory speed increases very much relied upon higher voltages and we saw manufacturers reaching settings in excess of 2.2v to achieve maximum performance. Things changed drastically overnight though when Intel launched a new architecture which limited voltage to 1.65v and at that stage memory manufacturers had to rethink their products. This is probably one of the least noticeable changes Intel have made for the average consumer but its effect is widespread because all modules released now meet that specification, even on kits designed for AMD systems.