My source is a IBM publication, PC and PS/2 Pocket Reference Manual
S41G-5086-00.  I quoted from it to try to answer the original question.
Of course, it may be wrong even though it's IBM.  Wouldn't be the
first time.  Also note that the value I quoted is described as the
"Sync Freq".  Could that be different from the scan frequency?
Anyway, to add perspective I've added the values given for the
IBM Color and Enhanced Color Displays below.  I interpret "EGA/CGD"
to mean "Enhanced Graphics Adapter set up to use the Color Graphics
Display".

>On 17 Jul 98 at 12:05, Neal Daskal wrote:
>
>> 5151  50/16.257khz  Mono
   5153  60/15.750khz  Color
   5154  60/15.750khz  EGA/CGD
         60/21.8khz    EGA/EGD
>
>  The PC video FAQ I found shows 18.43kHz horizontal for both MDA and
>CGA, but I could've sworn that CGA was 14.something -- in that
>awkward range where most men can't hear it, but most women can (and
>find it irritating).
>
>David G