Dear tsuwm: The quote from Quinion has the kind of information I was looking for:
"David Crystal described a simple
research project—using random
pages from a dictionary—that
suggests these figures are severe
underestimates. He concludes that a
better average for a college graduate
might be 60,000 active words and
75,000 passive ones. But this
method of assessing vocabulary
counts dictionary headwords only; it
would be possible to multiply it
several-fold to include different
senses, inflected forms, and
compounds. Another assessment—of
a million-word collection of
American texts—identified about
38,000 headwords. Bearing in mind
this was all general writing, this
doesn’t sound so different from
David Crystal’s estimates for
graduate vocabularies."

Which seems to mean that my guesstimate was not too wild, that I might actually be able
to use properly if not define exactly almost every tenth word in a dictionary. So I would
not be immodest to believe my vocabulary is in the 50 K range. And I would not hesitate
to suggest that yours is substantially greater than that, since you have been in the word
business for past ten years.