That looks realistic according to my experience, Peter. But use of deep contrast filters will complicate any predictability at long exposure quite a bit, in a manner that short exposures do not. The spec sheet doesn't give a clue about filter factors. Their wedge spectrum is based on tungsten light exposure, not daylight, so one has to somewhat careful interpreting it. I simply tried generic filter factors similar to FP4, HP5 etc, and it seemed to work.
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