HDDs now do like 80-150 (true) random read IOps - SSDs go towards 100.000 or even a million (enterprise products). The Intel SSD is between 50.000 and 80.000 depending on what review you trust. But as you see - you won't fix this with a little more rpm.
Maths is surprisingly not my best subject, but i guess you could calculate how many rpm a HDD has to be in order to compete with SSDs on random I/O. I guess this would be a very large number.
Even lower than 0.1ms actually, and it can process multiple I/O's at once which HDDs cannot do. Intel SSDs for example use the NCQ feature meant to shorten HDD access times on multi-queue I/O - is now being used to provide command queueing (buffering) so the SSD actually gets enough 'work' to perform like it should - while otherwise the SSD would not get enough I/O requests to saturate its 8 parallel flash channels.
HDDs are dying; they will soon not be used anymore for the system drive - banished to storing large bulky files only - until SSDs are matured to a point all storage will become electrical/solid state.