Some info from the little gray cells of a moderately old man.
1.) I had a 1953 Hudson Hornet with Twin-H Power (2 2bbl carbs) and a 4 speed hydro-matic. Pretty dam quick for a big old sedan. You could not break that tranny. One of the few with a rear pump so you could push start it.
2.) Aunt and Uncle had a 1956 Pontiac Star Chief with the 289 V-8 and 4 speed hydro-matic. They pulled 2-horse trailers all over Calif to shows and up to the Sierra's camping and hunting. Went through two motors at 100,000 each and still had the original HM when the car was sold.
3.) If you look up some early Gass Class drag cars, you will see the hunt for 1956 Chevy Sedan Delivery (only) cast iron case 4 speed hydro-matics which had the lowest gear sets ever offered and the Chevy bolt pattern. These obviously brought high dollars in the used market, were extremely durable and sought after. Paired with a screaming built 327 and you had a real race car.
4.) I raced in D Gas with a early 'Cuda. 273 bored to close to 292 and Torqueflite. We regularly "Neutral Started" that car on slicks with a 8.75 Mopar rear with 3.91's and it lived for a long time. That is we'd bring the motor to revs (~3,200) and drop in into gear on the last yellow and stand on throttle. The clutches would do their job and we'd be off. Never broke the case or the output shaft. That was THE toughest auto tranny I've ever known. Prolly tougher than the TH400's I run now.
They eventually outlawed Neutral Starts with TQFlites because no one else could do that. The "outlaw" lead directly to the development of the "ClutchFlite" which was a TQFlite with a engine driven external pump and a real clutch in a bell housing. These left on the clutch but shifted all auto down track. They also left at much higher revs - like 4,500 behind a big Dodge Wedge.
4.) I worked a Virgil Whitaker's garage after school in HS (early 1960's). We had a pretty good tranny guy. When he serviced the older auto trannies for things like bad front seals (very common), he had to keep the drained fluids in closed drums or the would attract animals. I assume that was the whale oil blended into the fluid ...
5.) International Harvester used TQFlites in their light and medium duty trucks behind everything from 345 2-BBL motors to their bigger intermediate 477's in medium duty trucks. The next choice was Allison for a bunch more. I do not know of a "Corn Binder" truck that broke a TQFlite...
6.) Early 1960's Ramblers had push button shift too. But it was hooked to a Ford auto and not nearly as strong as the TQFlite. Ran and felt similar, but was not a TQFlite. Did have an all aluminum 327 tough. Made lite power in some boats built up with Interceptor parts ...
The transaxle autos used in Corvairs and Tempests were Borg-Warner built tranny's. very nice actually. the Tempest unit would make a decent tranny for a well balanced home built sports car. They could handle at least 350 HP as my bud had a 63 Tempest with a built 326 that would break axle shafts (half shafts) but never broke the tranny, even on Atlas Plycons (poor mans cheater slicks back then)
7.) Lots of modern racers with big HP and high stall converters in TH400 tranny's running well down into the big 8's in the 1/4 with full steel bodies swear by Type F fluid in GM trannys'... They claim firmer and more predictable shifts. These are guys leaving with daylight under the front tires and and running < 1.40 60ft times.
8.) The thing that makes Power Glides work is the converter and the nearly indestructible nature of the tranny. A properly maintained PG is nearly as hard to break as a TQFlite.
The lowest aftermarket gears you can get for a PG are around 2.86. Not much compared to TH350 and 400's. But they are lighter and sap less parasitic HP loss (about 1/2). They are no good in heavy cars. But in a light car (< 2,500 say) making big power with a 5,000 stall converter, they can haul your butt down the track.
Lots of us run boring Chevron ATF (pick your poison) and get long tranny life. No one knows what's in it, but it works