You don't give the option of only "come", for either male or female. For me the old usage [come] works fine, and I'm afraid I look on "cum" as being not only vulgar but illiterate. We don't need it. And you go on to ask the hard questions about "cumming", "cummed" etc. - the latter even sounds illiterate. Come, come!
I think cum has to do with orgasm but not necessarily ejaculate. Some people don’t squirt but they definitely come! Also, coming implies an active process (coming or going). So to cum means one is getting “there” or at least try to go somewhere specific. Orgasm is definitely implicated. Some people never arrive at orgasm so therefore they did not cum.
Only males "cum"; *both* can "come". Since, as we already stated in earlier polls, "come" is the verb, while "cum" is a noun. But then you can then verb the noun, "to produce [noun]".