Yes, this is the "problem". I'm looking at my Bessa R2S right now. It's max ISO setting is 3200. So normally, at that setting, you would push the film three stops to get to 24000.
Now, assume I load in this 24000 with the ISO set to 3200. If I still have a totally negative light reading at 1.4 (my Nikkor 5.0cm's widest aperture) at a "steady hand hold speed" of 1/60 how do I guesstimate what my real settings should be 3 stops up?
I guess if I can get a reading of some kind at that setting I can just increase the shutter speed three steps or so? Would require a bit of trial and error.
This could be a fun dilemma to "play" with. I suspect that it will be important to make sure that your camera can be set to "in between" speed settings w/o "blowing up" before getting too exact! 😱