Thanks to all for your responses. I'll reply at this time but hope to
hear from more people. Here are my thoughts based on your responses so
far. It may take several posts to do this since there is a lot of
information in the replies.

The basic law of survey research is, pretest your questions on a small
group before using the questions on a larger group. This was not
possible in this context, with predictable result that the phrasing of
my question could have been improved on. It us now clear that what I
should have asked was something like, "In your personal experience,
with the kinds of globulars and galaxies you usually observe ,from the
kinds of skies you usually observe from, what do you find is the minimum
aperture that gives you satisfying results on globular clusters and
galaxies? You may answer separately for globular clusters and galaxies,
if you wish."

I posted my query on the yahoo talking telescopes group and on the
Astromart equipment forum, so there are responses from a broad range of
people.

I had also checked into three classic books on observing from the days
when small refractors were about all thatwere available, that is before
the six inch reflector, equatorial mounted was being widely built by
amateurs, and before reflectors became easily commercially available,
and of course long before the era of SCTs and Dobs.
William Tyler Olcott, in the 1909 "In Starland with a Three Inch
Telescope" says of M13 "is well worth observing... It takes a 4-inch
glass to catch the twinkling of the stars." Olcott and Mayall in Field
Book of the Skies" (1929, 1954) say "It is easily discernible in an
opera glass but it takes a 4-inch telescope to resolve its stars."
Bernhard, Bennett and Rice, in "New Handbook of the Heavens" (1941,
1948) say of M13: "The outer stars are resolved in a small telescope
and with a larger glass the entrancing beauty of the great globe of
stars is revealed."

So much for the classic view before the advent of modern amateur telescopes.

The responses I received to my posting were rich and complex. See Part 2
Ciao,
Bill Meyers