Bob, I'd really like to see some professional's answers to you question.
I can only offer the opinion of a hobbyist using a smaller lathe. (9"
Sheldon) If everything else is the same; power, rigidity, cutting speed
& direction, size and kind of metal, tool bit, finish, etc. etc. then as
you well know, for any particular operation there is a 'best and max'
combinaton of feed and depth of cut to remove the most metal per minute.
IMO, charts & tables [& ng's ] give us useless info re what's 'best'
for small machines and workpieces. For me, it's intuition from many
failed cuts and tries til the lathe complained.

I think your premise is correct, but trouble is that things are never
equal. Ex: greater depth of cut to get under the skin of cast iron will
remove more metal per minute or long thin spindle= less depth & greater
feed vs short thick blank= deeper depth & less feed. YMMV, but remember
I'm a rank amateur. Regards, Arch