The only handle I have on tonality is to plot the D/H curves of the
negatives for various developpers. Now mainly, the shape of the curve is
determined by the design of the film,  but you can easily change the
overall slope of the curve by changing the development time.

For example, Kodak 4147 Plus-X has an enormously long toe (some people
say it is all toe), and there is not much you can do about it other than
switching to another film if you do not like that. Kodak's TMY film in
XTol 1+1 has essentially no toe at all; i.e., its D/H curve is
essentially a straight line. Careless workers, or those working under
conditions where it is not possible to make careful exposures, hate this
characteristic because any underexposure results in total loss of shadow
detail.

There are subtilities, however, that are influenced by the developper,
however. For example two bath development in something like D-25 for
bath 1 and 2% Sodium metaborate for bath 2 will raise the toe a lot and
leave the higher zones relatively unaffected. Some people like that, but
I do not.

Only you know, implicitly, what you like and what you do not. There is
no really good way to discuss this in ASCIIland. What I suggest is to
make controlled exposures using the same film (whatever you like best,
perhaps), using different developers until you find the correct EI for
each and the correct development time. Plot their D/H curves, and them
print them on your favorite paper and evaluate the results. Then repeat
with 4147 Plus-X and TMY, and plot the D/H curves again. Then print from
such negatives and see which you like best. You will then know if you
like long-toe film (tolerant of underexposure, but weak in maximum black
and shadow detail), or short toe. You will know if you like a bump in
the middle of the curve or not, and so on.

Since few darkroom users seem willing to do these fundamental tests,
they mostly are whistling in the cemetary at midnight, and that is
unprofitable. But if you do this work, you, at least, will know what you
are talking about. And that will set you apart from the crowd.

Well, if it were objectively quantifiable there wouldn't
be much point talking about it ... since we can all blab
for hours on the subject there must not be any 'there' there.

To my mind, differences in contrast or characteristic
curve are not differences in 'tonality', they are differences
in contrast and characteristic curve: there is nothing to
discuss.

Tonality, to me, is the difference in the smoothness of the tone
and is best described as the differences in look between large and
small format.  With a good film/developer combination the grain
will be invisible in 8x10's made from either format.  But the
4x5 will have that 'look'; there is no doubt which photo was
taken with which format.

I think that once contrast and curve shape are matched
'tonality' is a function of the resolving power of the film -
even when the limit in system resolution is the lens.

I come to this conclusion from experimenting to find just how
close TMX in Microdol-X was to TechPan in Technidol.  (My
conclusion: not close at all.)

I took pictures of a resolution target tacked to a fence in
an outdoor scene and at the bottom of the chart I had pinned
the standard Kodak Grey scale - 10 zones in 10 inches
(or thereabouts).  I used this to insure both films were
exposed/developed for the same contrast.

In Photos taken at 40ft the 1" size of the grey scale zones
was close but within the resolution of either film, B/W bars
at the same spacing were sharply delineated.

Both films resolved the bars to the same level, implying that
the Micro Nikkor was the limiting factor.  Looking at just
the black/white resolution bars the prints looked the same.

However:

The patches on the grey scale were distinct with the TechPan but
a white-grey-black blur with T-Max.  The two grey scales when put
next to each other they match in density so contrast is not the cause.

The look of the scenery was very different:  The TMX has that same
old 35mm look to it, grainless but 'blah'.  The TechPan print
looked 'crisp' with a very smooth (here's the word) tonality.

My conclusion is the ability to spacially resolve small changes in density
is what gives TechPan it's large-format look.  

I can only speculate that the much higher resolving power of TechPan (600 lpmm)
over TMX (150 lpmm) that is the cause of this effect, even when the
system resolution is limited by the lens.

Interestingly TechPan shows more grain but it is very sharp and very uniform.
The T-Max grain is nigh invisible but it looks like oatmeal.

Result of experimentation: I now have a freezer full of
150ft rolls of TechPan.

Lens quality has a lot to do with it. More than you think.

I suppose a technical analysis of tonality could be when choosing a
particular film/developer combination and exposing it with a 35mm camera, a
medium format camera and a 8x10 inch large format camera. When enlarged onto
a sheet of  11x14 inch paper, the print from the medium format negative will
have a noticeably smoother looking transition of tones than the one from the
35mm negative while the contact print from the large format negative will
have the smoothest and most realistic detailed look about it, and yet each
of these prints may be satisfyingly good.
A high quality camera and enlarging lens are of course very important as
well as giving the correct exposure and development of the films when
processing.
The use of a sturdy tripod and a shutter release cable can make a very
significant difference between a hand held camera shot too.
Certain film and developer combinations are very well matched and there are
often out cries when a particular film stock is discontinued, I read an
article written by Geoffrey Crawley recently, who remembered a professional
photographer that he once knew, who was so annoyed when Ilford discontinued
FP3 in favour of FP4, that he sold up his business and moved on.
I know of one photographer who will not use anything other than FP4 plus
developed in Perceptol diluted 1:1 and no other paper than Ilford Gallerie
developed in Bromophen despite how good modern variable contrast papers are
these days. Because I live in the UK, I am wondering if there are any long
term Tri-X users who prefer the old Tri-X to the latest version. I believe
Tri-X is some thing of a cult emulsion amongst many B&W photographers who
live in the USA, and is deservedly popular.
To be honest with you Lloyd, provided that your current films, papers and
processing chemicals are yielding images that please you, then I wouldn't
bother to change, as long as you like them, then that is all that matters.
Enjoy your photography.