I'm curious-- what is the practical dynamic range of film such as TMX? I'm not referring to torture tests where people try +15 stops of overexposure to prove the film can still retain detail, but for a real world scene, how much range can TMX handle?
Well, what do you call practical? My personal work experience has been, by far, mostly with Kodak professional color negative portrait films. These have had, for many years, a very "substantial" latitude for overexposure. But what range is "practical?"
The outfit where I worked owned and operated a couple thousand portrait studios in the US and Canada. They were all set up with more or less standard lighting and exposure configurations. But... with that many locations, and enough employees to staff those studios, well... "rare" screw-ups were seen on a regular basis. Maybe on a monthly basis one studio, somewhere, would shoot a half-week's worth of portraits without their lens being stopped down. The resulting film would be about 4 or 5 full stops overexposed.
So what would be the result? Well, for the most part, neither the customer nor the studio people would notice any difference. But in the processing lab these negatives would take near ten times longer exposure times. So none the lab people wanna get stuck printing those rolls - they get bored of the longer exposures. And it drastically slows down the printer production rate - not as much as you might think, but probably by half, or so. A printer that could normally expose maybe a thousand 8x10s per hour is down to perhaps four hundred per hour.
So it works, but we didn't see it as practical. Another note, these films had a comfortable underexposure latitude of a stop or so, depending on the subject matter. So the exposure latitude was somewhere around 6 full stops or so. This would be with a typical subject luminance range (as printed) of around 8 or 9 stops. Meaning that the entire usable "luminance recording range" of these films was around 14 to 15 full stops. But is this a "practical" range? No.
Obviously your question was about a b&w film, not color, but maybe this will help put things in perspective. People would generally consider the pro b&w films to have a greater exposure latitude than color neg, but I've never actually done the tests.
I should put a slight disclaimer on the color neg results. These are with specific professional color neg films, used under studio flash. This is the "correct" color balance for these films, meaning that the three primary color layers are exposed in a proper balance with each other. If you were to expose under a different "color temperature" light part of the exposure latitude would be used up by the exposure offset between the film's color layers. So the usable latitude is reduced. One other thing should be said... these results were done in cine processors where agitation and developer volumes are not an issue. I'm pretty sure that Jobo users would not be able to match these results, largely because of sparse development - not enough developer to handle 5 stops of overexposure.
