I had looked at it as:
High Flow - engine can't heat the water as much as it would if the flow
were slower and there was more time to heat the water, resulting in less
temp rise in water across engine and more uniform temps in the block.
Water emerges from block not much hotter than it went in.  Water doesn't
stay in the radiator long enough to be exposed to air flow long enough
to be cooled very much.  Good news: it doesn't *have* to be cooled much
- it's not all that hot.
Low Flow - coolant spends more time in engine and gets hotter.  Greater
dT across engine block, coolant hotter exiting engine and entering
radiator.  Radiator has to draw more heat out of the coolant to get it
back to acceptable block entry temp, but has more time to do it on
account of lower flow.
What I hadn't seen, is how apparently wide a range of flows would
produce acceptable results.  I suppose a better radiator (more flue
area, better air flow, etc. - better cooling per in^3) would reduce the
volume requirement.  Lower limit on flow would seem to be that flow at
which the temperature gradient across the engine becomes unacceptable.
Thanks for the details ... Jim S.