Just curious, but why do you need such a slow film in sheets? The reason for tolerating a very slow film, for me, was to get very fine grain.
On more of a 35mm way of thinking, it is an aperture driven thing. From the Sunny F16 Rule: At EI 25 in sunny conditions f2=1/1600 second. At EI 100 in sunny conditions f2=1/6400 sec. The fastest shutter speed on my camera is 1/2000 second so a 25 speed film is a good choice for wide open apertures. For me a film like Kodachrome 25 or Panatomic-X would see a fair amount of use. It is a pity that Kodak doesn't think so. If I try to use a 100 speed film, I have lost what are to me some very desirable apertures on my lenses. I have been using a fair amount of Efke 25 for these situations.
"She's always out making pictures, She's always out making scenes.
She's always out the window, When it comes to making Dreams.
It's all mixed up, It's all mixed up, It's all mixed up."