Ah. I see what you mean. Just googling about with "i5 ram mhz 1333 or 1600" i5 and i7 memory controllers run at 1333 anyway. So unless you overclock, 1600 is pointless. I might overclock it do at some point though. So paying the extra couple of quid is no biggy.
RPM measurement alone is only important if you like watching things spin very quickly. Actually noise levels are what is of interest/concern, measured "against" RPM. And that is only meaningful if we also know what kind of performance we get at that rpm ( thermal performance or perhaps energy/$cost ). Silver Arrow…